Settings for Equalizer behaviour on small

Added functionality to determine what Equalizer will do on viewports <641px. Current behaviour once the elements Equalizer is watching become stacked is to set the height to inherit, however with this new functionality will allow users to specify Equalizer to continue making the elements it is watching an equal height.

Check out this thread on Foundation Forum on the discussion behind this: http://foundation.zurb.com/forum/posts/7483-equalizer-column-height-when-stacked-not-equalising
Various changes

Heading hierarchy has been refined.

Content hierarchy has been refined.

Documentation added for new Equalizer setting. See issue #4977 (https://github.com/zurb/foundation/pull/4977)
Merge branch 'master' of github.com:winghouchan/foundation into winghouchan-master

Conflicts:
	js/foundation/foundation.equalizer.js
Merge branch 'master' of github.com:zurb/foundation

Conflicts:
	js/foundation/foundation.equalizer.js