doc: refactor figure numbers into references

doc: refactor figure numbers into references

This change adds automatic figure references to the docs. The
figure numbers in the generated Html and PDF docs are now
automatically numbered based on section.

Requires Sphinx >= 1.3.1.

The patch makes the following changes.

* Changes image:: tag to figure:: and moves image caption
  to the figure.

* Adds captions to figures that didn't previously have any.

* Un-templates the |image-name| substitution definitions
  into explicit figure:: tags. They weren't used more
  than once anyway and Sphinx doesn't support them
  for figure.

* Adds a target to each image that didn't previously
  have one so that they can be cross-referenced.

* Renamed existing image target to match the image
  name for consistency.

* Replaces the Figures lists with automatic :numref:
  :ref: entries to generate automatic numbering
  and captions.

* Replaces "Figure" references with automatic :numref:
  references.

Signed-off-by: John McNamara <john.mcnamara@intel.com>