Merge pull request #204 from matthid/razor_4

Initial Razor 4 support.
Initial Roslyn Support:
- Changed some internals to make supporting Roslyn easier
- Added Roslyn support via extra package (RazorEngine.Roslyn) as we need additional references and Roslyn doesn't work on net40.
- Breaking Change: IAssemblyReferenceResolver -> IReferenceResolver (and interface changed as well). We never did a release with this interface so everything should be fine.
- We now support direct assembly references (as well as in-memory ones), this only works with Roslyn of course.
Update docs generation with the latest changes.
Documentation added:
- The custom FSharp.Formatting and FSharp.Compiler.Service build
- How to use Roslyn
- How the build process works and how to use it.
Lift a breaking change (Errors property on TemplateCompilationException)
Fix some Obsolete warnings pointing to old properties.
Don't try to generate debug symbols on mono.
disable roslyn unit tests on mono.
Update docs
Update release notes.
small doc fix.