Sitecore 7 support and fix for addedfiles metadata

I branched off from Nancy to include the post-install step but I also had to do a few more things to make it work nicely with Sitecore 7+: 
* up the framework target to 4.5
* register the handler in the <customHandlers>

I also patched the zip entry data parser to properly include addedfiles. 

If you accept these feel free to push them further upstream.