Document BIO_printf family

=pod

=head1 NAME

BIO_printf, BIO_vprintf, BIO_snprintf, BIO_vsnprintf

- formatted output to a BIO

=head1 SYNOPSIS

 #include <openssl/bio.h>

 int BIO_printf(BIO *bio, const char *format, ...)

 int BIO_vprintf(BIO *bio, const char *format, va_list args)

 int BIO_snprintf(char *buf, size_t n, const char *format, ...)

 int BIO_vsnprintf(char *buf, size_t n, const char *format, va_list args)

=head1 DESCRIPTION

BIO_printf() is similar to the standard C printf() function, except that

the output is sent to the specified BIO, B<bio>, rather than standard

output.  All common format specifiers are supported.

BIO_vprintf() is similar to the vprintf() function found on many platforms,

the output is sent to the specified BIO, B<bio>, rather than standard

output.  All common format specifiers are supported. The argument

list B<args> is a stdarg argument list.

BIO_snprintf() is for platforms that do not have the common snprintf()

function. It is like sprintf() except that the size parameter, B<n>,

specifies the size of the output buffer.

BIO_vsnprintf() is to BIO_snprintf() as BIO_vprintf() is to BIO_printf().

=head1 RETURN VALUES

All functions return the number of bytes written, or -1 on error.

For BIO_snprintf() and BIO_vsnprintf() this includes when the output

buffer is too small.

=head1 COPYRIGHT

Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use

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

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.

=cut

UI_get0_action_string() is used to retrieve the action description

associated with a B<UIT_BOOLEAN> type B<UI_STRING>.

For all other B<UI_STRING> types, NULL is returned.

See L<UI_Add_input_boolean(3)>.

See L<UI_add_input_boolean(3)>.

UI_get0_result_string() is used to retrieve the result of a prompt.

This is only useful for B<UIT_PROMPT> and B<UIT_VERIFY> type strings.