Use better markdown for domintro sections

Use bikeshed markdown shortcuts to simplify file:

* Use : and :: for dt/dd (in markdown and other dls)
* Combine div class=note/dl class=domintro tags where possible
* Use |name| instead of <var>name</var>
* A few other one-off markup/markdown switches

Verified (via copy/paste of browser-rendered spec to text files) that there are no text differences as a result of this.

Author: inexorabletash