Make the indexer a server like YCM

[ankrgyl]

YCM avoids managing its state with Vim by running a separate server. They're also clever about how they kill it- they kill the YCM server if no YCM command has been run in 12 hours. This way you can spin up the server in the plugin if it's not already running, and not have to worry about cleaning up its state.

[ankrgyl]

This is more of an issue now that there's C++ background threads that crash when you quit the vim process.