Update style.css
Add class attribute for all browsers in thematic_html

See https://github.com/ThematicTheme/Thematic/commit/4a62381a929ef8f8ac70915c9a1af1d2cc090d72#commitcomment-3505475
Update readme.txt

Add a more generalized message.
Merge branch 'master' of git://github.com/SeamlessThemes/Thematic into SeamlessThemes-pull40

Closes #40