* ext/openssl/ossl_hmac.c: [DOC] Documentation for OpenSSL::HMAC
  based on a patch by @repah documenting-ruby/ruby#14
  https://github.com/documenting-ruby/ruby/pull/14


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42416 b2dd03c8-39d4-4d8f-98ff-823fe69b080e