Merge with NicoSantangelo/SublimeLinter-contrib-flow

Hello! sorry for the delay!

I finally got around [merging](https://github.com/NicoSantangelo/SublimeLinter-contrib-flow/issues/2) the packages. I've splitted the commits in the different features so you can review them separately (and if you don't like any of them, rebase and remove them).

Try it out if you like! if anything looks suspicious let me know, I'm happy to help.

Thanks! 
Can you remove this? I don't think its needed since linter plug-in needs to use 'File-only' mode and flow will search on its own for the `.flowconfig`