Guts: Override in-page TOC for type reference

That TOC was literally about six screens long. On a big monitor. Blow it away
and make a smaller multi-columned one, so you can see the start of the page from
the get-go! This isn't the most sustainable way to do this, but it at least
solves the worst of the fugly.
Revise preamble text of type reference to be more useful for beginners

- Cover the basics
- Link to language reference
Update 3.3.0-rc3 type reference w/ recent changes to generator
Clarify further about testing for undefined variables with lookupvar et al