Summary:
For block-level elements that have a margin-top or margin-bottom set
(generally to 12px), also reset the appropriate margin to 0 when
they're a first-child or last-child of their parents.
The change doesn't affect nested lists, their selector is more specific.
Test Plan:
Look at some comments or wiki documents that end with different
block elements, verify that the margins are pretty.
Reviewers: epriestley, #blessed_reviewers, chad
Reviewed By: #blessed_reviewers, chad
Subscribers: Korvin, epriestley
Projects: #remarkup
Maniphest Tasks: T6968
Differential Revision: https://secure.phabricator.com/D11382
2297a43d44