Support for local VCS allowing to index local path

[olczykkrzysztof]

Support for local VCS allowing to index local path not necessarily being a part of the version-controller repository.

Non-copying version of https://github.com/etsy/hound/pull/138.

[jklein]

This looks good to me, thanks. I'll let @kellegous take a look and merge when ready.

[kellegous]

@gemignani Sorry, I have been really behind on pull requests. I'll take a closer look at this soon. I'll leave some minor comments now. I think the one thing that is missing in the local support is that local vcs really shouldn't poll by default because it introduces the possibility that the repo will be indexed while it is being mutated. However, that's a thing I can easily help out with.

[snagytx]

Any plans to finish this support?

[olczykkrzysztof]

@snagytx, I'd love to, but very short time recently. :(