Enhance Template Parser Class Writeup in User Guide

Added two additional sections to the writeup: template parser usage notes, and view fragments.
Clarified a couple of "pseudo-variable" references.

Verified sphinx build.
Signed-off-by:James L Parry <jim_parry@bcit.ca>
The lines look uneven in length with your changes ... we have a soft limit of ~70 chars per line, can you try to "align" them all to that length?