(parser) new highlightAll() API

[joshgoebel]

Progress towards #2277.

Changes

Added new highlightAll() API which deprecates:

• initHighlighting()
• initHighlightingOnLoad()

These are slated to be removed with version 12. (with v11 they will likely just because aliases to highlightAll())

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The new function can be called at any time and will "just work".

• If called after DOM has loaded, it will immediately highlight.
• If called before, it will wait until the DOM finishes loading, then
  highlight.

If there are any cases where highlightAll() is needed prior to the DOM onload firing, we can discuss those cases between now and v12. That would seem to be an edge case though I'd guess and could easily be handled with a custom unload handler.

Checklist

• Added markup tests, or they don't apply here because...
• Updated the changelog at CHANGES.md
• Added myself to AUTHORS.txt, under Contributors

[egor-rogov]

Good thing!