Reorganise asn1.h and add comments.

# define V_ASN1_OTHER                    -3/* used in ASN1_TYPE */

# define V_ASN1_ANY                      -4/* used in ASN1 template code */

# define V_ASN1_NEG                      0x100/* negative flag */

# define V_ASN1_UNDEF                    -1

/* ASN.1 tag values */

# define V_ASN1_EOC                      0

# define V_ASN1_BOOLEAN                  1 /**/

# define V_ASN1_INTEGER                  2

# define V_ASN1_NEG_INTEGER              (2 | V_ASN1_NEG)

# define V_ASN1_BIT_STRING               3

# define V_ASN1_OCTET_STRING             4

# define V_ASN1_NULL                     5

# define V_ASN1_EXTERNAL                 8

# define V_ASN1_REAL                     9

# define V_ASN1_ENUMERATED               10

# define V_ASN1_NEG_ENUMERATED           (10 | V_ASN1_NEG)

# define V_ASN1_UTF8STRING               12

# define V_ASN1_SEQUENCE                 16

# define V_ASN1_SET                      17

# define V_ASN1_GENERALSTRING            27 /**/

# define V_ASN1_UNIVERSALSTRING          28 /**/

# define V_ASN1_BMPSTRING                30

/*

 * NB the constants below are used internally by ASN1_INTEGER

 * and ASN1_ENUMERATED to indicate the sign. They are *not* on

 * the wire tag values.

 */

# define V_ASN1_NEG                      0x100

# define V_ASN1_NEG_INTEGER              (2 | V_ASN1_NEG)

# define V_ASN1_NEG_ENUMERATED           (10 | V_ASN1_NEG)

/* For use with d2i_ASN1_type_bytes() */

# define B_ASN1_NUMERICSTRING    0x0001

# define B_ASN1_PRINTABLESTRING  0x0002