add: resolve links to symbols in markdown descriptions

[carsakiller]

Links like [mySymbol](lua://mySymbol) in a comment will now be resolved to a URI pointing to the actual file where mySymbol can be found.

I would also like to add highlighting and completion while you are writing so that [something](lua:// triggers completion of symbols – but I'm not sure where to even start for that.

This change will result in @see being pretty much useless. I never really used @see much due to formatting issues and it not looking quite right. Perhaps @see should be removed?

Closes #2175