Identify which tag dictionaries each tag belongs to

[hegemonic]

We currently have two tag dictionaries: The JSDoc tag dictionary and the Closure Compiler tag dictionary. Right now, if you look at the docs for an individual tag, it's not always clear whether a tag belongs to the JSDoc dictionary, the Closure Compiler dictionary, or both. We should make this as clear as possible. We should also clearly spell out the syntax that each dictionary supports for each tag.

Ideally we'd do this in such a way that it's easy to add new dictionaries to the docs in the future.