Add FSharp compiler and MSBuild files.

These were originally found at C:\Program Files (x86)\Microsoft SDKs\F#\3.0\Framework\v4.0
Tell FSProj to use your copy of the FSharp.Targets.

Be careful here. Simply replacing the original reference will make VS unhappy. You have to add it as a seperate Import entry and add a guard clause to the original Import.
Fix hint path for Antlr3
Provide the FSharp.Core assembly to the compiler components
Redirect FSharp.Targets to use the tool exes from your repo.
Link against the FSharp.Core.dll that we packaged with the compiler.

I couldn't get the NuGet package to work because if the lack of the sigdata file. BUT since we packaged the core dll with the build we can just use that!