!!! WIP
This implements the "genec" layer wrapping mbedtls + openssl
ECDH support.
API tests are added for the parts that are implemented so far.
Stuff related to ec at all, like keys, are prefixed lws_genec_.
Stuff specific to ECDH are prefixed lws_genecdh_.
Although RSA can be used directly for signing / JWS
on large chunks of data since it's only operating on
the hash, when JWE support arrives, which allows bulk
encryption, it's going to be mandatory to support
secondary AES ciphers to use on the bulk data.
This adds generic support for all AES modes that OpenSSL
and mbedTLS have in common, works on both mbedTLS and
OpenSSL the same, and adds unit tests for each mode
in api-test-gencrypto, to run in CI.
