Some 2.1 docs missing

reported [on gitter](https://gitter.im/bitovi/canjs?at=5515af53c183f73134d075e5): http://canjs.com/2.1/docs/can.mustache.html

Start by opening the reported 2.1 URL, http://canjs.com/2.1/docs/can.mustache.html, and compare it with the surrounding CanJS documentation. Identify what is missing and how adjacent documentation is organized. Done means the missing 2.1 documentation is available at the reported URL and matches the surrounding docs.

Written by the indexing model from the issue text.