mbedtls has older and newer hashing apis, if we detected the newer ones
we use them like the older ones since generally, hashing doesn't have a
way to fail for sha and md5 update etc.
Coverity objects... change it to dumbly check the retcode.
!!! 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_.
Like the simple hashes, these work the same regardless of if the backend is
OpenSSL or mbedTLS.
Also move into ./lib/tls/ and split into two specific to mbedtls or openssl
backends.
