Adding Interoperable RA-TLS support to RATS-TLS

This is the task list we need to complete in order to implement the Interoperable RA-TLS proposal on RATS-TLS.

[x] Initial support for Interoperable RA-TLS X.509 DICE certificate format, with evidence extension. #123
[x] Add support for endorsements extension. #135
[x] Put <pubkey-hash> in claims-buffer instead of userdata field of evidence. https://github.com/inclavare-containers/rats-tls/pull/144
[x] Write a document of the steps required by compatibility tests between RATS-TLS and other projects.
[ ] Support endorsements extension for occlum mode. https://github.com/occlum/occlum/issues/1102
[x] Support minimal set of hash functions: sha-256 (ID 1), sha-384 (ID 7) and sha-512 (ID 8) #147

inclavare-containers / rats-tls