Config yaml

Hi,

I converted my json config reading functions to yaml, as discussed in #34. (This adds the PyYaml libraries to the list of dependencies).

I haven't tried to integrate it into the rest of the code this time, as i still haven't fixed my issues with tox and i remember my previous try breaking a lot of tests (this new pull request might break a few as well, hopefully not too much).

I'm also not sure how to deal with global testing once it's integrated, since most core functions will probably depend on the config file and might mess with the actual user's config when running the tests...

It's quite useless right now, but I don't want to mess with the rest of the code before i can make sure i'm not trashing too much of what's already there, so here goes.