Tweak the description of CC0, remove notes about the PDM, and other non-controversial technical corrections.

* Slightly tweak the description of CC0 at the top and add some more information at the end.
* Remove the additional notes on the Public Domain Mark from the end, as agreed.
* Put "CC0 Public Domain Dedication" in title case.
* Use curly quotes.
* Add a missing "the" and a missing period.
CFPB's qu project uses the language now