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.

scripts/tally.toy

@@ -0,0 +1,21 @@
+fn makeCounter() {
+	var counter: int = 0;
+
+	fn increment() {
+		return ++counter;
+	}
+
+	return increment;
+}
+
+var tally = makeCounter();
+
+while (true) {
+	var result = tally();
+
+	print result;
+
+	if (result >= 10) {
+		break;
+	}
+}