Include some features to highlight some texts in gist notes

Dear team,
If there is some features like coloring, italic etc... in Gist, will help many people to highlight the things included in there notes, codes etc...

The issue names no files, tests, or entry points. Start by locating the Gist note editing and rendering entry points, then clarify which formatting features and scope are intended. Done means the agreed text-highlighting features work in Gist notes and are covered by appropriate tests.

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