Mostly doc changes and some bug fixes

Use render() instead of a local wikifier, making it possible to render DOM directly in special passages

Trims trailing spaces.

Fixes #1704.

This reverts merge request !5960

SugarCube repository moved from BitBucket to GitHub migrating from
Mercurial to Git. Hence the update for the guide.

Teach SugarCube to avoid cloning the state object when history size is
equal to 1

Define save descriptions uniformly for the entire game, instead of using nonsense everywhere that's not the main page.
Patch Sugarcube to skip creating passage excerpts (which can be expensive) when descriptions are predefined.