Package as a Xamarin component

Adds all of the packaging magic to build a Xamarin component package out of Akavache. It should build cleanly on Mac if Akavache is built before running the tools. 

Right now, it needs a better icon, and maybe to have some of the copy updated in Details.md and GettingStarted.md.

I'm also not sure about the Powershell bits, as I don't have Windows around and set up--I'll try and get it set up to build this soon.