Rename `is-container: container` => `role: nest`
Update changelog
Merge branch 'susy-next' into full-row

* susy-next:
  Update changelog
  Rename `is-container: container` => `role: nest`

Conflicts:
	docs/changelog.rst
	sass/susy/language/susy/_rows.scss
	sass/susy/language/susy/_settings.scss
	test/css/ag.css