Make header tags bolder
more correct heading for author dist list
use bootstrap includes for retina images
handle variable resolution better on plussers page
line plussers up with rest of sidebar
small cleanups to contributors list

Avoid contributors section contracting when animating showing the list.
Also size the links in the contributors list better.
less/css/js/images should not be executable
Configure travis to build on 5.20
Allow failures on 5.20 for now
Close div tag in wrapper
use https for all cpan.metacpan.org links
Merge pull request #1288 from haarg/fix-author-heading

more correct heading for author dist list
Merge pull request #1293 from haarg/more-https

use https for all cpan.metacpan.org links