Rename project, possibly marked-enhancements

[jhoffner]

marked-extensions isn't a good name anymore, especially since marked has its own extensions system. marked-enhancements might be an ok name, since we are offering a set of general enhancements. The enhancements are all related to improving code challenge documentation, so maybe something more specific, like marked-code-challenge-instructions would be better?

Probably need some discussion around this

[kazk]

marked-extensions wasn't a good name because it's vague. I think it only works as an umbrella package that reexports smaller ones. marked-enhancements is very similar.

@codewars/marked-challenge-doc?