Tweaked macro error messages

* The error messages should now mention the origin macro more
consistently. (The <<set>> macro still cannot, as its 'run' method is
also used by setter links.)
* Code macro error messages should no longer include converted
Javascript error listings that are nigh-unreadable to most users.
* Implemented support for the data-setter property to inline HTML, as
introduced by SugarCube.
* Made the error message colour slightly less saturated in Sugarcane.
* Fixed an obscure bug: where <<else if ...>><<endif>> tags were flush,
the <<endif>> was seen as missing.