Add missing EVP_MD documentation

=head1 NAME

EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy_ex,

EVP_MD_CTX_ctrl, EVP_MD_CTX_set_flags, EVP_MD_CTX_clear_flags,

EVP_MD_CTX_test_flags, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,

EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy,

EVP_MD_CTX_copy_ex, EVP_MD_CTX_ctrl, EVP_MD_CTX_set_flags,

EVP_MD_CTX_clear_flags, EVP_MD_CTX_test_flags,

EVP_Digest, EVP_DigestInit_ex, EVP_DigestInit, EVP_DigestUpdate,

EVP_DigestFinal_ex, EVP_DigestFinalXOF, EVP_DigestFinal,

EVP_MD_CTX_copy, EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size,

EVP_MD_block_size, EVP_MD_CTX_md, EVP_MD_CTX_size,

EVP_MD_CTX_block_size, EVP_MD_CTX_type, EVP_MD_CTX_md_data,

EVP_MD_type, EVP_MD_pkey_type, EVP_MD_size, EVP_MD_block_size, EVP_MD_flags,

EVP_MD_CTX_md, EVP_MD_CTX_type, EVP_MD_CTX_size, EVP_MD_CTX_block_size,

EVP_MD_CTX_md_data, EVP_MD_CTX_update_fn, EVP_MD_CTX_set_update_fn,

EVP_md_null,

EVP_get_digestbyname, EVP_get_digestbynid,

EVP_get_digestbyobj,

EVP_MD_CTX_set_pkey_ctx - EVP digest routines

EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj,

EVP_MD_CTX_pkey_ctx, EVP_MD_CTX_set_pkey_ctx - EVP digest routines

=head1 SYNOPSIS

 void EVP_MD_CTX_clear_flags(EVP_MD_CTX *ctx, int flags);

 int EVP_MD_CTX_test_flags(const EVP_MD_CTX *ctx, int flags);

 int EVP_Digest(const void *data, size_t count, unsigned char *md,

                unsigned int *size, const EVP_MD *type, ENGINE *impl);

 int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);

 int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);

 int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s);

 int EVP_MD_pkey_type(const EVP_MD *md);

 int EVP_MD_size(const EVP_MD *md);

 int EVP_MD_block_size(const EVP_MD *md);

 unsigned long EVP_MD_flags(const EVP_MD *md);

 const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);

 int EVP_MD_CTX_size(const EVP_MD *ctx);

 int EVP_MD_CTX_block_size(const EVP_MD *ctx);

 int EVP_MD_CTX_type(const EVP_MD *ctx);

 void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);

 int (*EVP_MD_CTX_update_fn(EVP_MD_CTX *ctx))(EVP_MD_CTX *ctx,

                                              const void *data, size_t count);

 void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,

                               int (*update)(EVP_MD_CTX *ctx,

                                             const void *data, size_t count));

 const EVP_MD *EVP_md_null(void);

 const EVP_MD *EVP_get_digestbynid(int type);

 const EVP_MD *EVP_get_digestbyobj(const ASN1_OBJECT *o);

 EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx);

 void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);

=head1 DESCRIPTION

=item EVP_MD_CTX_ctrl()

Performs digest-specific control actions on context B<ctx>.

Performs digest-specific control actions on context B<ctx>. The control command

is indicated in B<cmd> and any additional arguments in B<p1> and B<p2>.

EVP_MD_CTX_ctrl() must be called after EVP_DigestInit_ex(). Other restrictions

may apply depending on the control type and digest implementation.

See L</CONTROLS> below for more information.

=item EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(), EVP_MD_CTX_test_flags()

Sets, clears and tests B<ctx> flags.  See L</FLAGS> below for more information.

=item EVP_Digest()

A wrapper around the Digest Init_ex, Update and Final_ex functions.

Hashes B<count> bytes of data at B<data> using a digest B<type> from ENGINE

B<impl>. The digest value is placed in B<md> and its length is written at B<size>

if the pointer is not NULL. At most B<EVP_MAX_MD_SIZE> bytes will be written.

If B<impl> is NULL the default implementation of digest B<type> is used.

=item EVP_DigestInit_ex()

Sets up digest context B<ctx> to use a digest B<type> from ENGINE B<impl>.

Returns the B<EVP_MD> structure corresponding to the passed B<EVP_MD_CTX>.

=item EVP_MD_CTX_set_update_fn()

Sets the update function for B<ctx> to B<update>.

This is the function that is called by EVP_DigestUpdate. If not set, the

update function from the B<EVP_MD> type specified at initialization is used.

=item EVP_MD_CTX_update_fn()

Returns the update function for B<ctx>.

=item EVP_MD_flags()

Returns the B<md> flags. Note that these are different from the B<EVP_MD_CTX>

ones. See L<EVP_MD_meth_set_flags(3)> for more information.

=item EVP_MD_pkey_type()

Returns the NID of the public key signing algorithm associated with this

Returns an B<EVP_MD> structure when passed a digest name, a digest B<NID> or an

B<ASN1_OBJECT> structure respectively.

=item EVP_MD_CTX_pkey_ctx()

Returns the B<EVP_PKEY_CTX> assigned to B<ctx>. The returned pointer should not

be freed by the caller.

=item EVP_MD_CTX_set_pkey_ctx()

Assigns an B<EVP_PKEY_CTX> to B<EVP_MD_CTX>. This is usually used to provide

a customzied B<EVP_PKEY_CTX> to L<EVP_DigestSignInit(3)> or

a customized B<EVP_PKEY_CTX> to L<EVP_DigestSignInit(3)> or

L<EVP_DigestVerifyInit(3)>. The B<pctx> passed to this function should be freed

by the caller. A NULL B<pctx> pointer is also allowed to clear the B<EVP_PKEY_CTX>

assigned to B<ctx>. In such case, freeing the cleared B<EVP_PKEY_CTX> or not

=back

=head1 CONTROLS

EVP_MD_CTX_ctrl() can be used to send the following standard controls:

=over 4

=item EVP_MD_CTRL_MICALG

Gets the digest Message Integrity Check algorithm string. This is used when

creating S/MIME multipart/signed messages, as specified in RFC 3851.

The string value is written to B<p2>.

=item EVP_MD_CTRL_XOF_LEN

This control sets the digest length for extendable output functions to B<p1>.

Sending this control directly should not be necessary, the use of

C<EVP_DigestFinalXOF()> is preferred.

Currently used by SHAKE.

=back

=head1 FLAGS

EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags() and EVP_MD_CTX_test_flags()

Returns 1 if successful or 0 for failure.

=item EVP_MD_type(),

EVP_MD_pkey_type(),

EVP_MD_type()

EVP_MD_pkey_type()

Returns the NID of the corresponding OBJECT IDENTIFIER or NID_undef if none

exists.

=head1 SEE ALSO

L<EVP_MD_meth_new(3)>,

L<dgst(1)>,

L<evp(7)>

=item EVP_MD_FLAG_ONESHOT

This digest method can only handles one block of input.

This digest method can only handle one block of input.

=item EVP_MD_FLAG_XOF

This digest method is an extensible-output function (XOF) and supports

the B<EVP_MD_CTRL_XOF_LEN> control.

=item EVP_MD_FLAG_DIGALGID_NULL

EVP_MD_FLAG_DIGALGID_NULL, the latter will be overridden.>

Currently unused.

=item EVP_MD_FLAG_FIPS

This digest method is suitable for use in FIPS mode.

Currently unused.

=back

EVP_MD_meth_set_init() sets the digest init function for B<md>.

The digest init function is called by EVP_DigestInit(),

The digest init function is called by EVP_Digest(), EVP_DigestInit(),

EVP_DigestInit_ex(), EVP_SignInit, EVP_SignInit_ex(), EVP_VerifyInit()

and EVP_VerifyInit_ex().

EVP_MD_meth_set_update() sets the digest update function for B<md>.

The digest update function is called by EVP_DigestUpdate(),

The digest update function is called by EVP_Digest(), EVP_DigestUpdate() and

EVP_SignUpdate().

EVP_MD_meth_set_final() sets the digest final function for B<md>.

The digest final function is called by EVP_DigestFinal(),

The digest final function is called by EVP_Digest(), EVP_DigestFinal(),

EVP_DigestFinal_ex(), EVP_SignFinal() and EVP_VerifyFinal().

EVP_MD_meth_set_copy() sets the function for B<md> to do extra

EVP_MD_CTX_free().

EVP_MD_meth_set_ctrl() sets the control function for B<md>.

See L<EVP_MD_CTX_ctrl(3)> for the available controls.

EVP_MD_meth_get_input_blocksize(), EVP_MD_meth_get_result_size(),

EVP_MD_meth_get_app_datasize(), EVP_MD_meth_get_flags(),

=head1 COPYRIGHT

Copyright 2015-2017 The OpenSSL Project Authors. All Rights Reserved.

Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy