Metadata - Second Iteration (Incomplete)

- worked on #123
Bug fixes

- Fixes issue where private sealed class SZArrayHelper is not allowed in
namespace, must be nested.
- Fixes issue where the compiler doesn't know what to do with some of
the extern methods marked as Internal Calls.
- Fixed bug in CILTransformationStage for the CallVirt instruction where
constraints weren't properly handled.
Merge pull request #125 from charsleysa/metadata

Metadata - Second Iteration (Incomplete)