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
It still means we'd end up sometimes giving you the generated content (the times we actually recompile the page). Let's solve this separately as part of the other issue - https://github.com/aspnet/Mvc/issues/895.