SVG Travis, and Coverage badge in docs [ci skip]

The SVG badge uses the Shields project for consistency with other projects' badges.
More info:
http://blog.travis-ci.com/2014-03-20-build-status-badges-support-svg/
Fix alt text [ci skip]
Merge pull request #613 from hugovk/patch-2

Badges: SVG Travis, and Coverage in docs [ci skip]