Fixed minor syntax issues.
Requires an `.is-sticky` class on each element, rather than using a global style.

This allows us better control to have different behavior between media
queries, etc.
Pulls initialization code into a re-usable method.
Re-initialize div array on page resize, since originally calculated offset will no longer be accurate.
Always re-render stickies after building sticky array.
Kills some whitespace.
Merge pull request #183 from DoSomething/sticky-fixes

Sticky fixes