NuGet package for WP8 projects targetting x86/ARM can now be built with MSBuild

To build and publish package to a given NuGet repo:

C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe sqlite-net-wp8.msbuild /property:NuGetServerApiKey=<mysecret> /property:NuGetServerAddress=<mynugetserver>