Refactor gen_rpc, implement 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.

priestjim / gen_rpc