Qemu builder

I added an issue for a pure qemu builder. This pull request provides an initial implementation for that issue: Issue #384.

I will support the testing and requests against this builder. As it operates qemu-system-x86_64 directly, it has to perform some management usually handled by external apps, for instance VBoxManage or similar. In any event, it tests out ok and has a working sample set of configurations in the documentation (website) markdown.