Make grammar styling a bit nicer

[domenic]

http://tc39.github.io/ecmascript-asyncawait/#AsyncFunctionDeclaration-static-semantics could be prettier:

Some ideas (brainstorming):

• Don't allow breaking in component parts, e.g. "[no LineTerminator here]" should always stay on one line.
• New line and indent after the colon?
• Turn off linebreaking entirely? (Be careful this doesn't break mobile.)
• Try to make line breaks consistent, either by the author inserting them or by some heuristic? E.g. a line break before each of "function" and "{AsyncFunctionBody}" might work.
• Change the font or font color or...?