* Fix dump_keywords to require attribute docs
* Change the documentation commands to make definition files positional
Since the definition files are mandatory, make them positional
parameters instead of options.
We have some common code used by several docs scripts. Migrate that
into the build-only shared code repository.
* Move lib/ansible/utils/_build_helpers.py to the directory for common
build code
* Migrate docs/bin/dump_config.py to a build-ansible subcommand
* Migrate dump_keywords to the build-ansible framework
* Make the script more maintainable by using functions and good
variable names
* Port to Python3 idioms
* Fix bug so that private attributes will be undocumented
* Move generate_man to a build-ansible subcommand
* Port plugin_formatter to a build-ansible subcommand
* Rework command_plugins so that docs scripts can target Python-3.4+ and
releng-only subcommands can use more recent versions of Python.
The architecture is now that command_plugins/* need to be importable
on Python-3.4. The init_parsers() method needs to run on Python-3.4.
But the main() method can utilize features of more recent Python as
long as it fits within those parameters.
* Update docs build requirements
Port the plugin_formatter to build-ansible framework
