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.

tests/scripts/test_closures.toy

@@ -0,0 +1,22 @@
+//closures
+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;
+	}
+}

tests/scripts/test_fibonacci.toy

@@ -0,0 +1,20 @@
+
+fn fib(n) {
+	if (n < 2) return n;
+	return fib(n-1) + fib(n-2);
+}
+
+assert fib(1) == 1;
+assert fib(2) == 1;
+assert fib(3) == 2;
+assert fib(4) == 3;
+assert fib(5) == 5;
+assert fib(6) == 8;
+assert fib(7) == 13;
+assert fib(8) == 21;
+assert fib(9) == 34;
+assert fib(10) == 55;
+assert fib(11) == 89;
+assert fib(12) == 144;
+
+print "Fibonacci passed";