This change adds a module which builds documentation using Sphinx.
Documentation files and assets are defined using a pw_doc_group GN
template which lists out all of the sources as metadata. Another GN
template, pw_doc_gen, collects the metadata from pw_doc_group targets
into a JSON file and defines an action that runs a script to build the
HTML docs.
A docgen script is provided by the pw_docgen module. This script reads
the JSON metadata file collected by a pw_doc_gen template, copies all of
the source and resource files into a documentation tree, and runs Sphinx
on the tree to render the docs as HTML.
Change-Id: I97890f05d850d5119cbd3bbf48138cd82f22d56c
