appveyor - continous build

Hi Neil,

Pull request contains appveyor configuration. 

Create an secure nuget api key to push the package to nuget.org 

Appveyor provides a tool to create encrypted keys 
https://ci.appveyor.com/tools/encrypt

Once this ready, replace the place holder in the appveyor.yml with that value and everything should work.

I have configured the rest of the things in appveyor account.

Cheers,
Karthik