Refactor including SSL support

• The server and acceptor FSMs have been converted to gen_statem to
  follow Erlang's best practices
  and development. As a result, support for Erlang releases older than
  19.1 has been dropped.
• Specific options, leveraging Erlang 19, have been enabled such as
  off-heap mailboxes for client and acceptor,
  and higher priorities for all gen_rpc processes.
• Ports are not dynamically assigned anymore as it shows that, after
  some research, offers no additional benefits
  to having a static port listener. That means less processes to
  supervise and less moving parts where something can
  go wrong.
• Support for SSL has been added. Please refer to the
  README for more information on
  how to use it.
• Module version control support has been added, effectively allowing
  you to only make RPC calls to nodes that
  run specific versions of modules.
• lager support has been dropped in favor of the logging
  backend-agnostic library hut, in order to better support
  Elixir installations. The test suite and development profiles still
  use lager but this doesn't interfere with production
  deployments of gen_rpc.
• Tests have been updated to test more edge cases, including new SSL
  functionality.
• Some options in gen_rpc.app.src have changed names to better
  describe what they do. Again, pleaserefer to the README to
  verify your preexisting settings are consistent with their new names.
• Various smaller bugs have been fixed and various responses have been
  massaged for consistency.