[WIP] Add iodine integration

[ojab]

Travis is failing due to https://github.com/boazsegev/iodine/issues/45

1. Is it ok to just declare Litecable::Server in lite_cable/iodine_server.rb or should I implement some kind of Litecable.iodine!?
2. What interface ClientSocket::Base should provide? Right now iodine one quacks mostly like existing one, but iodine doesn't provide on_error callback, for example (to be clear: I mean recommended rack.upgrade api here), so it's not completely the same.
3. AFAIU it's not possible to test both implementations in one go, so there is envvar to test iodine implementation.