Implement Repo Deletion

[triplem]

Since I needed this one anyway, and the one implemented in #19 contained unnecessary fixes as well, we keept it simple and do one thing per PR.

[dergachev]

That's a scary rm -rf in there.... anyone have an idea of how to do this safer?

[tainewoo]

maybe it's better to use FileUtils.remove_entry_secure :

http://ruby-doc.org/stdlib-1.9.3/libdoc/fileutils/rdoc/FileUtils.html#method-c-remove_entry_secure