A possible re-working of Usecases.
Add a references section.
Revise the "Sources" section and add references.
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
Merge branch 'edit-usecases' into big-merge
Merge branch 'edit-sources' into big-merge

Conflicts:
	protocol.rst
Remove a duplicate reference target.
Remove the "Components" section.
Tweak formatting

GitHub didn't like my definition list style with the dimdict keys.
Add table-of-contents

Woo!
Add an example for dist={0: 'b', 1: None}.
Fix code-block-title formatting.
Clarify map definition.

Requested by @wfspotz.
Fix errors in dimdata summary table.
Tweak language around padding.

Add "boundary padding" and "communication padding" to Definitions section, though the definitions are currently TODO.
Make a couple of minor formatting tweaks.
Merge branch 'merge-and-remove-components' of https://github.com/enthought/distributed-array-protocol into merge-and-remove-components
Merge branch 'merge-and-remove-components' into add-examples
Add Unstructured example.
Rewording.