Make RSA_sign.pod less confusing.

PKCS #1 v2.0 is the name of a document which specifies an algorithm
RSASSA-PKCS1-v1_5, often referred to as "PKCS #1 v1.5" after an earlier
document which specified it. This gets further confusing because the
document PKCS #1 v2.1 specifies two signature algorithms,
RSASSA-PKCS1-v1_5 and RSASSA-PSS. RSA_sign implements RSASSA-PKCS1-v1_5.

Refer to the document using the RFC number which is easier to find
anyway, and refer to the algorithm by its name.
Reviewed-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NRich Salz <rsalz@openssl.org>

GH: #1474

doc/man3/RSA_sign.pod

@@ -17,9 +17,9 @@ RSA_sign, RSA_verify - RSA signatures
 =head1 DESCRIPTION
 
 RSA_sign() signs the message digest B<m> of size B<m_len> using the
-private key B<rsa> as specified in PKCS #1 v2.0. It stores the
-signature in B<sigret> and the signature size in B<siglen>. B<sigret>
-must point to RSA_size(B<rsa>) bytes of memory.
+private key B<rsa> using RSASSA-PKCS1-v1_5 as specified in RFC 3447. It
+stores the signature in B<sigret> and the signature size in B<siglen>.
+B<sigret> must point to RSA_size(B<rsa>) bytes of memory.
 Note that PKCS #1 adds meta-data, placing limits on the size of the
 key that can be used.
 See L<RSA_private_encrypt(3)> for lower-level