tweak readme [ci skip]

* Drop remaining links to the Github wiki
* Redirect Mailing list links through the wiki
* Update links that are redirects
* enable syntaxhighlighting
update all wiki links
Show avatar of recent user in conversation list
Fix hashtags that start a line when posting to Facebook or Twitter, by applying all the same options to strip_markdown as applying to markdownify, fixes #3768 and #4154
Merge pull request #4240 from jaywink/3768-hashmark-first-character

Fix hashtags that start a line when posting to Facebook or Twitter
Merge pull request #4244 from svbergerem/4237-consistent-conversation-list

Show avatar of recent user in conversation list

Conflicts:
	Changelog.md
fixed #cat-footer overlay