Adding Microsoft Edge and the rendering engine EdgeHTML.

Closes #18303
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provide V4 JSBin template for users to use when sending bug reports.

As Slack is a common replacement for IRC for projects (e.g. Wordpress), I propose that we encourage the use of Slack as you have members of the core team using it while IRC often does not have any of the core team available.

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Refs #12352, which is now implemented & deployed.
More info: https://github.com/twbs/savage

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Based on https://github.com/twbs/rorschach/tree/master/docs

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Fixes https://github.com/twbs/bootlint/issues/67

Thanks to @collinanderson
Closes #14567

Refs: #14109

Fixes #12657

Removes outdated coding style rule.

Parts of the "Pull requests" section are strangely worded.

This commit fixes that.

Hey look, I'm contributing to CONTRIBUTING.md!

This anchor must have been overlooked while updating the docs in a previous commit. Expected behavior: scroll the document to a linked section. Experienced behavior: nada.

This proposed file change renames the anchor text from `coding conventions` to `coding guidelines` and changes the anchor link from `#code-conventions` to `#code-guidelines`.