Multiple updates to support local development and civibuild

Created by: totten

Buildkit includes a configuration for docs, but it doesn't work well during setup because nothing will be initialized until you enter in some secret URLs.

This adds a single command, bin/console docs:publish, which publishes everything listed in the *.yml files.

Additionally, this PR allows you do work more directly on the books, e.g.

• Use parameters.yml to set publisher_repos_dir. This way your books don't live inside the var/cache/ directory (which gets deleted every now and then... which is a bit annoying...).
• Use bin/console docs:serve to setup a temp HTTP server with live-reload support.