Introduced methods which provide a clear interface for registering and querying for index and instance types. This is now the interface that snippets and related modules should use to get access to a type object that manages an instance type. Eliminated the use of a static variable in the snippets class for this purpose, which was always asking for trouble because of http://justjs.com/posts/singletons-in-node-js-modules-cannot-be-trusted-or-why-you-can-t-just-do-var-foo-require-baz-init