Add tests (without performance hit)

I close #11 and start over here without `glob` because of a performance hit. This version is basically on par with the speed of current master.

This should be enough to serve as a basis for discussion.
I sort the walkdir results, added first (very simple) tests, activated travis ci builds, and added badges to the readme.
Tests pass on travis ci and on a local windows vm.

I'm not sure if it's necessary/desired to test API and CLI seperate, but currently that's what I do.

Added dependencies: mkdirp
Added devDependencies: mocha

If you were to merge this, you would have to activate atom/asar in travis ci.

What's missing?

- More tests obviously. (But feedback first.)
- Appveyor windows builds. (I have to read a little bit about it first.)
- "clean"-script
- `file.type` is currently string, could be optimized

So, feedback? Questions? Change requests?

Have a nice day.