Support daemon mode

[HybridEidolon]

Racer now has a daemon mode which, as of 1.1.0, has some progress towards caching syntax completion information. It is started with the daemon command and receives the usual commands through stdin.

[edubkendo]

I don't current use atom or rust, so I probably won't be adding features to this plugin. I certainly welcome pull requests though.

[sunxfancy]

I'm trying to make the daemon mode support, but the tips gui won't show until the process shutdown, does anyone know the reason? My fork is here: sunxfancy@6b1888e