consider replacing actix-web

[jeremyandrews]

It's unclear what the future of actix-web is, consider replacing with another backend.

Requirements:

• allows streaming (need to be able to open an audio stream from the client while it's being recorded and start processing on the server in real-time)
• allows sharing data between threads (initialize deepspeech once and share with a mutex)
• JSON
• stable Rust (I really like Rocket, but I'm not interested in using unstable Rust: possibly just wait for the 0.5 release w/ Stable support)
• minimal dependencies are preferred as possible

There's no particular requirement for performance at this time, as Kakaia is intended to be run on a private network where the current assumption is there's minimal clients making requests.

[jeremyandrews]

The actix-web project has resumed with a new maintainer, as well: https://github.com/actix/actix-web/issues/1289