Document "get/set-app-data" macros.

Document "get/set-app-data" macros.

Documenting the macros removes 14 undocumented items.
Merged three separate manpages into one.
Rename the DRBG CRYPTO_EX define into RAND_DRBG, but keep the old one
for API compatibility.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10216)