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/fib.toy

@@ -1,15 +1,12 @@
-//BUG: Not yet functional
+//tentatively functional
 
-//example of the fibonacci sequence
-fn fib(n: int) {
+//fibonacci sequence
+fn fib(n) {
 	if (n < 2) return n;
 	return fib(n-1) + fib(n-2);
 }
 
-//TODO: type coercion syntax hasn't been decided on yet, but it will be needed
-for (var i = 1; i <= 10; i++) {
-	print i .. ":" .. fib(i);
-}
+print fib(12);
 
 //Note to my future self: yes, the base case in 'fib()' is 'n < 2', stop second guessing yourself!
 //Note to my past self: don't tell me what to do!