remove unused `{{ page.base_url }}` variables, and fix the urls

Combine multiple .thumbnail > img styles

Change tense to imperative

Matches this comment with the commit messages and other comments.

JS comments pointed to new documentation

Add -moz-osx-font-smoothing

Remove execute permissions on fonts files.

Ditch amp

Chrome for OSX print issue with select tags

Variable way to set caret width

Add .animation() mixin

* Since we removed the z-index of our default navbars in 76baacf2, we no longer need this warning.
* A quick test of the new code showed no problems with dropdowns falling behind a sibling navbar, so folks should be good to go.

Add another newline to improve final code readability

This divides banner from code.

Document that uncollapsing the mobile navbar requires JS

QUnit.equals() is deprecated; use QUnit.equal() instead

Kick up grunt-contrib-jshint dependency