Flesh out the introduction a bit

Change-Id: I0bd5d0b26c19251fd8512a14c2c0e5d3160e239d
Shuffle things around in the Key Negotiation section

Split into subsections for clarity, and move the cross-reference
to the first instance of AFSCombineTokens.

Change-Id: Ie22e85e64780a49fcb2b042fe654fa8636250c8e
Move Authenticator Data up and edit

Reformat to a better indentation level, and mention that this
is the authenticator of the rx challenge/response exchange, for
clarity.

The goal is to get all the tiny bits which are just specifying
application-specific rxgk behavior at the front of the document,
and the newer ~extensions later.

Change-Id: I59e537a399ac4e73ab2e21714fd63ab3e5078351
Some edits to the Tokens section

Change title, add intro, random nits.

Change-Id: Idb63ba1a9db6d60e308c7d7f4abd3d08fd109ebd
Switch to new token format

Separate identity lists for user and CM identities.

Change-Id: I75bcbfce1320833aa92f696c51fc35587ad8e267
Update the Cache Manager Tokens section

Give better motivation and introduction, change some handling,
and mention that combined tokens could be used in a pinch
(but it's a bad idea).

Change-Id: I25d0ad76ac46feb5a86cacffad4bf4d143b498f0
Add a section on CombineTokens

Specify the remaning bits that weren't in the core document.

Change-Id: Ice787a86d5d8f65fbc9ad4ba8c7d3819c5272ade
Update AFSCombineTokens

Remove some content that is redundant with elsewhere.
Change variable names for the input tokens.
Describe identity handling.
Do not attempt to assign an RPC number; that will be done by
the registry, since the RXGK package is already created.

Change-Id: I8b9e3c84b543e36609b1bb2792a3227702eb9434