Propogate additional compilation data from RoslynCompilationService

* Update CompilationFailedException to include path of file being compiled
* Pass in path being compiled to Rolsyn.
* Adding doc comments for compilation pieces

Fixes #869
Would something like this work - https://github.com/aspnet/Mvc/blob/dev/test/Microsoft.AspNet.Mvc.Razor.Test/RazorViewTest.cs#L244?

```
var expected = 
@"Compilation failed:
hello
world";