Convert heat.common.template_format to use C yaml

Will fall back to pyyaml if CSafeLoader/CSafeDumper are not available.
This should increase template parsing performance by a factor of 9 and
reduce memory usage by an order of magnitude.

We also convert the one test that was directly calling yaml to use the
template_format.parse function, so that the same parsing is used
everywhere.

Change-Id: I0d14be2ef7fb2dccac43fc41b1d2d9e4395c6f77
Fixes bug #1214580
Fix the main docs index page

This magic new line makes the main index look a lot better.
It wasn't showing the "HOT templates" level.

Change-Id: I3f7fb65911a4b0f3ad57ddf22c00ec8236261c7e
Merge "Fix the main docs index page"
Merge "Convert heat.common.template_format to use C yaml"