Add a section "NAMING CONVENTIONS".

Add a section "NAMING CONVENTIONS".

There is no need to explain well-known acronyms that are widely
used outside OpenSSL, too (like AES, ASN.1, CMS, ECDSA, PKCS...),
but OpenSSL uses plenty of idiosyncratic naming elements that
deserve to be explained (like d2i, ex, get0, ndef, sk, ...).

Requested by jsing@; feedback and OK tb@.