* plugin_reference is extended to build data for particular Plugin Base cls
* plugin_reference is extended to build data for all Plugin Bases (instead
of just building data for hardcoded classes).
* cli_reference is extended to build data for particular command
* new include_vars extension is introduced for including const data in docs
Change-Id: I76d9f85e41c6ab8e622f6d3581478962144525ba
