- Trace comments cover module items, decls, and stmts
- Added pseudo-lexer to Alex parser for monadic Position production
- Added Position to every DeclToken
- Removed Comment PackageItem
- Added CommentStmt and CommentDecl
- Fixed traversal skipping outer MIAttr ModuleItems
- Generally cleaned up Parser modules

This should make it much easier to add support for ``, `", macros with
arguments, etc., in the future.