Markdown fixes

[morags]

Added several languages and fixed a typo in markdown.tmLanguage.

[msftclas]

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[msftgits]

Hi, I am closing and re-opening this PR to bump the CLA bot. Sorry for the inconvenience!

[msftclas]

Hi @morags, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!
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[mjbvz]

Please update these to use the fenced code block logic that the other languages now use. It's rather horrific but it fixes a few important edge cases

[mjbvz]

Thank you for these improvements. They should be in the next insiders build

[morags]

Thank you.