Proposing documentation improvements

Hey, Paul

So, this is a proposal for improvements on parslepy docs.

I ended up giving up on moving stuff from the Wiki, because 1) it would be a lot more work than I thought, and 2) the Wiki contents seem to have more freedom, so it may be cool keeping it as a Wiki.

Here is a summary of the changes:

1. cleanup README leaving only the essentials (quick description, install and pointers to docs) and moving stuff to main docs (except TODO list that went to its own file)
2. beefed up the text for some explanations, added example at the top to peak interest =)
3. updated and tested examples given in Usage section
4. added shell-script for previewing and auto-compiling the sphinx docs, watching for changes in `docs/index.rst`

Does this look good?

Please let me know if there is anything you want done differently.
Elias