Tweak NEXT HISTORY.md entries formatting, groups, and add attribution

This tweaks the NEXT HSITORY.md entries in the following ways:

* Grouped them by CSS module.
* Moves (!) important ones to the top.
* Uses parenthises () instead of brackets [] to prevent Markdown links.
* Adds attribution for external contributions.
Merge pull request #59 from ericf/history-next

Tweak NEXT HISTORY.md entries formatting, groups, and add attribution