bake: Big pass on bake performance. - Reduce the amount of data passed between processes. - Make inter-process data simple objects to make it easier to test with alternatives to pickle. - Make sources have the basic requirement to be able to find a content item from an item spec (path). - Make Hoedown the default Markdown formatter.

--exclude=build
--exclude=dist
--exclude=docs/_cache
--exclude=docs/_counter
--exclude=bower_components
--exclude=node_modules
--exclude=docs/raw
--exclude=*.egg-info
--exclude=__pycache__
--exclude=__tmpfs__