Fix #124 Add support for RuleDelayed in maps

Context: Sometimes, Wolfram returns an error in the form of a RuleDelayed from `"MessageTemplate"` to an expression to get a human-friendly message. F.ex. evaluating `(list (w/Interpreter "City") "San Francisco, US")` while offline returns `Association[RuleDelayed["MessageTemplate", MessageName[Interpreter, "noknow"]]]`. We should do better than throw a parse exception. It has been decided to return the delayed expression as-is and leave it to the user to evaluate it (since calling eval during parsing is ugly). Action: Parse RuleDelayed just as Rule, only add a metadata :wolfram/delayed, for user's information.