!!! 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.
Several new ops are planned for tls... so better to bite the bullet and
clean it out to the same level as roles + event-libs first.
Also adds a new travis target "mbedtls" and all the tests except
autobahn against mbedtls build.
Private header stuff specific to roles should go in the
role dir and only be included if the role is enabled for
build.
Only definitions related to lws core should go in the actual
private-libwebsockets.h
