[documentation] Forms API: Multipart Forms and Documentation

[Angie Byron]

> After months of work between hunmonk, myself, and chx, we've finalized
> some substantial progress on multipart forms. A multipart form is a form
> that is spread across multiple pages (like a wizard), but doesn't truly
> "submit" until the final page.

This is awesome, you guys!

However, it brought to my attention that the Forms API portion of the handbook
is a right bloody mess. You have to dig down 60 levels deep to get to this great
document, which is no good at all!

So I made the following changes:

- Changed title of "Forms API Outline" to just "Forms API"
- In general, moved any documents that related to forms API itself, from this
point forward, with no legacy crap mentioned, under the top-level "Forms API"
item (so quickstart guide, reference, etc.)
- Kept anything specifically about updating 4.6 forms to 4.7 under "Upgrading to
forms API"
- Unpublished the Forms API Errata page (http://drupal.org/node/36055), since it
was basically useless.
- Moved Tips and Tricks to the top-level under "Forms API" and moved the couple
stray documents we had inside of it.

So now, the tree looks like:

Drupal APIs
= Forms API
  = Forms API Quickstart Guide
  = Forms API reference
  = Tips and Tricks
    = #tree and #parents
    = The #ref property
    = everything else that was already under tips and tricks
  = Upgrading to Forms API
    = Example module conversion: Project module (which probably should be burned
since I bet 200% of it is no longer valid since project module has changed so
much since I wrote this ;|)
    = Core module before and after examples
    = Flowcharts (renamed to Drupal 4.6 vs. Drupal 4.7 Forms API Flowcharts --
general flowcharts will eventually be created and moved under the top-level)
    = Forms API FAQ (probably should also be burned)

There might be a bit more clean-up here to do, but it's hopefully much easier to
find stuff now.

Uh, yeah. Sorry to take us totally OT. Thanks for the docs! :)
-Angie