[DOCS] Add* and run eslint-plugin-markdown

[hasezoey]

Summary

This PR basically adds* and runs eslint-plugin-markdown, including all changes required for this to work, in more detail:

• remove docs from being ignored in eslint completely
• apply eslint to test/docs
• add overrides to use env browser for docs/js/**/*.js
• apply eslint to docs/**/*.js (except *.min.js files)
• convert all javascript blocks with acquit-require in it to language acquit, to not confuse eslint with invalid tokens
• convert the eslint config from json to js to allow comments
• fix all documentation problems (like invalid tokens)
• apply eslint to all *.md files

*Note: eslint-plugin-markdown has been disabled with commit 6f2dec1, because of some out-standing issues: eslint/markdown#214

This PR (or the mentioned PRs if this is merged first) may require fixes:

• Update some scripts to be more consistently in place #13045
• Move doc generation scripts to proper places #13166
• Misc Documentation changes #13084
• Change API documentation headers to be more unique #13113

re #12691

[Uzlopak]

awesome

[vkarpov15]

Is there any way we can avoid this one indentation change? The indentation is slightly off here because the await assert.rejects() is stripped from the output because of // acquit:ignore:start, so we want the docs to appear as if await event.save() isn't indented at all.

[hasezoey]

we could disable indentation rule for that line, but would not recommend to to it globally

or the acquit (plugin?) could handle indentation changes between comments

[hasezoey]

for now i could add a quick-fix of ignoring the eslint rule (but editors may still automatically apply indentation)

or we could wait for vkarpov15/acquit-ignore#6