Add project parser

Adding a project parser to the F# compiler services avoids repeated inconsistent project file cracking by client tools.

When preparing for the F# compiler tutorials in NYC I wrote this project parser code.  It is very similar to @rneatherway's [project parser code](http://www.neatherway.com/project-references-msbuild.html) but also works on Mono - working around a couple of bugs in Mono 3.8.0.

Robin is going to take a look at this and integrate his work with it.