[T4] Add support for VS2012 host directive attributes
[RazorTemplate] Generate static helper methods
[T4] Update templates
[T4] Fix host directive visibility attribute
[MSBuild] Roundtrip sln VS version info
[MSBuild] Clean up up MSBuildFileFormat
[MSBuild] Add sample VS2010-2013 projects for tests
[MSBuild] Fix warning loading solutions contains ToolsVersion 12 projects
[MSBuild] Add tests for loading VS2010, 2010, 2013 projects
[MSBuild] Fix incorrect ToolsVersion check
[MSBuild] Test that there are no loading errors/warnings