More minor Remarkup tweaks
Summary:
Fixes T7444, Fixes T7963. A few small changes:
- Section headers are slightly larger
- Regular headers are slightly darker
- hr's have more padding, standard blue color
- code blocks now have correctly attached header colors
- Phriction emdeded links have color anchor color
Test Plan: Lots of various pages in Phriction, Diviner.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7963, T7444
Differential Revision: https://secure.phabricator.com/D12596