Add Release Notes and Roadmap

This adds Release Notes and Roadmap to the docs plus a couple of minor content updates.

Sphinx autodoc uses python's "import" to read the docstrings embedded in code.  To do so requires an __init__.py file and that the code be named ending in .py.   Thus, there's a challenge getting the docstrings from the actions/ directory.   Solution included here: in the docs/Makefile when building docs, we create a dummy __init__.py and symlink each <action> to <action>.py, let autodoc do it's thing, then clean up afterward.