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
do not use `cref="!:..."`.  this will get copied into the generated XML file and will indicate an _error_ to readers of that file.  relying on occasional case that errors get rendered as links isn't a good policy.

besides that, I don't think you meant to leave this in.  :smiley_cat: