TypeSystem API:

* Decide on the fate of ISupportsInterning (depends on how we're going to implement persistence)

* Try to build SharedTypes for void, int, etc.
	Take care of equality with the real System.Void, System.Int32 etc.
	This seems to be hard/impossible to do, see comment in SharedTypes.cs.
	I'm trying to work without those types now.
	
	Note that having shared type *references* is possible (typeof(int).ToTypeReference())

* Implement the C# parser producing the DOM
* Implement ResolveVisitor
* Implement all the nasty context-dependent stuff (local variables, lambdas) that CSharpResolver doesn't do (yet)
	Where should that go? I'd like to keep it out of CSharpResolver, that class is bloated enough with the pure logic.