Change supported browser versions to be "(current - 1) or newer" only for rolling-release browsers.

Also, added a note we support Opera 12.1x.
Make it clear we don't support browsers newer than current stable ones.
2.0.4
Update link for cdnjs on download page
2.0.5
Add recommendations for browser support resources.
2.0.6
Add links to VMs to save hunting.
2.0.7
HTML is not Markdown.
2.0.8
Added meetups page.
2.0.9
Don't specify a template for contentfull pages.
2.0.10
Index: Replaced Who's Using jQuery with Corporate Members logo rotation.
2.0.11
1.9 Upgrade Guide: AJAX -> Ajax
2.0.12
Docs: Removed IRC channel links in CONTRIBUTING.md

GitHub doesn't support links with the irc protocol, so these were dead links.