Removing unused file
Shortening some function names

They could be shorter and still readable
Adding a missing include path to YCM's extra conf
Initial version of omnifunc-based omni_completer

Still a work in progress (needs better triggering and bug fixes)
Removing YCM as omnifunc if no native support
Better triggering of semantic completion

Now there's a nice user-configurable setting for when YCM should trigger
semantic completion. This is very useful for the new omni_completer that uses
data coming from Vim's omnicomplete system.
Docs for the Completer API
Actually stopping compilation when no support

Previously we would just emit an error message _and continue_. The "and
continue" part was an embarrassing oversight.
The docs now reflect the new omni-completer

... and the new, fleshed-out Completer API.

YCM now provides semantic completions for every language that Vim has
omnicomplete support for, which is _a lot of them_.