Differentiate Remarkup header sizes more clearly
I think the design intent was to make it hard to make bad-looking documents, but all the headers end up being very samey.
Differentiate the sizes of the headers better so they're much more obvious (e.g., when scrolling through a document) and the different levels are more distinct.
This might be a little overboard, but we can always pull it back a bit if it's too much, and I think giving users more control in Remarkup (in cases where it doesn't create some weird syntax/parsing nightmare) is generally a good thing.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20569