Docs at  have already been converted from WADL (SGML / XML) to RST
using fairy-slipper .
This commit polish the results from the conversion and migrate the docs
to our repository under 'api-ref/source' directory. In addition, it
added missing descriptions for access_token_id and consumer_id to
Polishing the generated RST files include:
- Removing unnecessary blank lines;
- Removing empty references.
Polishing the generated RST files do not include:
- Modifying their content;
- Modifying file names;
- Wrapping lines at the maximum of 79 chars.
Updating the documentation will be done after this migration step.
This change also adds a tox environment to build the docs using sphinx
under 'api-ref/build', which in turn is added to '.gitignore'.
Lastly, 'os-api-ref' is added as a test requirement. It provides the
sphinx stanzas rest_method and rest_parameter, used to define OpenStack
APIs in RST docs.