allow top ribbons be position:fixed too

just add the "fixed" class to your wrapper and the ribbon will be fixed
(or static) in the corner, not scrolling away.

Fixes: #11
set the style of a:hover explicitely

if not set, the ribbon will inherit the hover style from (e.g., if used)
twitter bootstrap and become funny blue-ish and not as we want it.
Merge pull request #16 from evgeni/explicit-styles

set the style of a:hover explicitely
Merge pull request #15 from evgeni/fixed-top-ribbon

allow top ribbons be position:fixed too