Add ability to uninstall

[steve-thousand]

Would it be reasonable to add the ability to uninstall a package that has been installed via npm-install-version?

One of the uses I have for this library is the ability to install and compare multiple versions of the same module at run-time. It would also be useful to be able to clean up after I am done. Generally I think if we want to be able to install modules programmatically via this library then we should have the ability to uninstall as well. Wondering if it would take anything more than just an rm -rf of the module directory