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
nit: not much to distinguish fileContent from compiledCode.  be good to include a few details, such as a quick description of the processing applied to fileContent (Razor ...) to create compiledCode.