* src/ecdh.c: New file.
* src/Makefile.am (libntbtls_la_SOURCES): Add new file.
* src/context.h (ecdh_context_t): New type.
(_ntbtls_handshake_params_s): Use new type for 'ecdh_ctx'.
* src/protocol.c (handshake_params_init): Init ECDH_CTX.
(handshake_params_deinit): Deinit ECDH_CTX.
(ssl_write_hello_request): Rename to write_hello_request.  Change
caller.
* src/protocol-cli.c (write_supported_elliptic_curves_ext): Implement.
(write_cli_supported_point_formats_ext): Implement.
(write_client_hello): Call them.
(parse_supported_point_formats_ext): Implement.
(parse_server_ecdh_params): Implement.
(parse_signature_algorithm): Fix debug output.
(read_server_key_exchange): Improve debug output.
(write_client_key_exchange): Implement ECDHE key exchange.
* src/ciphersuites.c (_ntbtls_ciphersuite_list): Advertise ECDHE_RSA
key exchange.