libwebsockets

genec: generic ECDH crypto layer

!!! 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_.