0.3.0

Basically deals with #33 and #6 plus validation of cache scope [from config object](https://github.com/fgrehm/vagrant-cachier/blob/0.3.0/lib/vagrant-cachier/config.rb#L19-L29) instead of [erroring out](https://github.com/fgrehm/vagrant-cachier/blob/0.3.0/lib/vagrant-cachier/provision_ext.rb#L61) later on :)

I ended up not doing the cleanup on the code that I wanted but will get to that as soon as I have a chance.