Rewrite HMAC stuff to use HMAC_ apis instead of EVP
Bit trickly since modern OpenSSL has opaque HMAC_CTX and older
OpenSSL does not have any apis to allocate and free it.
Add another cmake check for the allocation api to decide
what to do.
!!! 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.
