Updated kvm homebrew

* Removed old kmono and kre formulae (are they still needed? It looked like they were not needed... @lodejard ?)
* Changed kvm to use the aspnet/kvm repo

Things to be done before this can be merged:
* [ ] Clarify the release branch for aspnet/kvm
* [ ] Use that branch in the stable variant defined here.

Tested the new formula on OS X 10.10, works fine.