Below RETURN VALUES,

Below RETURN VALUES,
* mention that EVP_MD_CTX_md(3) also returns NULL
if no message digest is configured yet; and
* omplete the list of functions returning const EVP_MD *,
also making the wording more precise.

Delete EVP_MAX_MD_SIZE from the NAME, SYNOPSIS, and HISTORY sections
because we do not usually document preprocessor macro constants in
this way.  There is nothing special about this constant justifying
an exception.