Functions are working, tests incomplete

This required a massive cross-cutting rework to the scope system,
multiple subtle bugfixes and relearning of the parser internals, but it
does appear that functions are working correctly.

A few caveats: for now, parameters are always constant, regardless of
type, return values can't be specified, and some script tests have been
written.

Most importantly, a key feature is working: closures.

source/toy_value.c

@@ -178,7 +178,7 @@ void Toy_freeValue(Toy_Value value) {
 			return;
 
 		case TOY_VALUE_FUNCTION:
-			//not sure this needs to be freed
+			Toy_freeFunction(value.as.function);
 			return;
 
 		case TOY_VALUE_OPAQUE: