Certificate Management Protocol (CMP, RFC 4210) extension to OpenSSL

Also includes CRMF (RFC 4211) and HTTP transfer (RFC 6712)

CMP and CRMF API is added to libcrypto, and the "cmp" app to the openssl CLI.
Adds extensive man pages and tests.  Integration into build scripts.

Incremental pull request based on OpenSSL commit 1362190b

 of 2018-09-26

1st chunk: CRMF API (include/openssl/crmf.h) and its documentation (reviewed)

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7328)