Backport v2 quoted literal "strings"/'strings' duality.

[Coco]

I reckon that porting back v2's behavior of allowing the usage of both " and ' when writing quoted literal strings won't really break existing code. The following(var := 'string') doesn't really work , so no such code exists and the following var := " a 'b' c" would still work. The current "" escaping should be retained obviously. Or if it's currently impossible, perhaps allow optional escaping of " by using a backtick(`) aside from consecutive "".