Remove Flattr for the time being.
About.md: Make links clickable.
Update jquery mousewheel to v3.1.12.
Update dependencies.
Update to Jekyll 2.3.x
Update dependencies.
Update Font-Awesome to v4.2.0.
Update 404.html to the latest html5 boilerplate version.
Switch to the Font-Awesome Paypal icon.
Update dependencies.
index.md: fix Bootlint error.
Update TreePropSheet's link.
Fix `.table-responsive` usage.

`.table-responsive` must have a `.table` child.
Update to Jekyll 2.4.x.
Add `transform: rotate(360deg)` for social links.
Add missing vendor property for IE 9.
Fix another Bootlint error.
Update dependencies.
Add grunt-bootlint in test.

This will make sure we actually use Bootstrap the proper way.
Fix another Bootlint error.