Edit main section

Edit the main section. Lots of changes here.

1. Formatting: use double backticks to indicate monospaced code-keywords
2. Split the first couple paragraphs off into the Overview section
3. Remove the monolithic "Distributed Array Protocol" heading and replace with subheadings.  Make the main title "Distributed Array Protocol v1.0.0"
4. Edit the keys needed for each `disttype`
5. Add a summary table for the disttypes and their required keys
6. Make an opinionated tweak to __version__ definition.  Kurt may disagree.
7. Remove the "Goal" section
8. Add some references