Make a MonoDevelop solution for fsharp-refactor

There are three projects in the solution:

  * FSharpRefactor, which contains the core library
  * FSharpRefactor.CommandLine, which contains the command line
    interface for the library
  * FSharpRefactorTests, which contains the tests

This should make it easier to integrate the project with FSharpBinding.
Update Makefile to use xbuild
Update .gitignore
Stop tracking mdb file