Finish adding support for AES-CCM mode

- Add #ossl_is_ccm macro for AES-128-CCM, AES-192-CCM and AES-256-CCM
- Modify OpenSSL::Cipher#authenticated? to return true for CCM modes
- Add ossl_ccm_set_auth_tag and ossl_ccm_get_auth_tag methods
- Modify OpenSSL::Cipher#auth_tag and OpenSSL::Cipher#auth_tag= to
support CCM
- Add OpenSSL::Cipher#iv_len= method to support non-standard CCM IV
lengths
- Add some documentation on how to use non-standard CCM IV lengths