The Streams API doc is now broken up into 3 sections:

1. API for Consumers
2. API for Implementors
3. Details and Extras

This addresses one of the biggest points of confusion for new users who
start to consume streams, and get the impression that they have to do
lots of extra work and implement classes and such, just to get some data
out of a file.

Noted in @shtylman's #3898, API stability notes are easy to overlook
in the html documentation. This can be especially troublesome if the API
is deprecated. This commit gives visual feedback by adding in a class
to the html docs when they're generated. The API headers with
corresponding colors are also listed in the 'About this Documentation'
page for easy reference.