Autolinking as specified by the GFM spec

[thehowl]

After some more research about how GitHub handles autolinking, I wound up finding the proper GFM spec. One of the goals of #3354 is that of porting over functionality, which was previously provided by JavaScript, into Go, which is why I do not intend to include this as part of the PR, seeing as that is already quite big. However, once it is merged, it might be good to replace the linkProcessor in modules/markup/html.go with a proper processor following the GFM specification - which should hopefully solve once and for all all issues regarding autolinking not working.

This would also fix #3095.

cc/ @ypnos

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.

[techknowlogick]

Closing per merged PR