RFR: Add markdown filtering

[Robin Westberg via github.com]

Hi all,

Please review this change that adds basic markdown filtering when forwarding hosted comments to mailing lists. This is far from a proper CommonMark parser, but should improve the readability of forwarded comments.

Best regards,
Robin

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Commits:
 - ad9ad423:	Add emoji support

Pull request:
https://git.openjdk.java.net/skara/pull/123

Webrev:
https://webrevs.openjdk.java.net/skara/123/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/123.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/123/head:pull/123