Implement function types / indirect calls / trampolines (#39)

tests/compiler/function-expression.ts

@@ -1,11 +1,37 @@
 var f1 = function(a: i32): i32 {
   return a;
 };
-f1(1);
+assert(f1(1) == 1);
+
 var f2 = (a: i32): i32 => {
   return a;
 };
-f2(2);
+assert(f2(2) == 2);
+
 var f3 = function someName(): void {
 };
 f3();
+
+function makeAdder<T>(): (a: T, b: T) => T {
+  return function theAdder(a: T, b: T): T {
+    return a + b;
+  };
+}
+
+var i32Adder = makeAdder<i32>();
+assert(i32Adder(4, 2) == 6);
+
+var f32Adder = makeAdder<f32>();
+assert(f32Adder(1.5, 2.5) == 4.0);
+
+function makeAdderArrow<T>(): (a: T, b: T) => T {
+  return (a: T, b: T): T => {
+    return a + b;
+  };
+}
+
+var i8Adder = makeAdderArrow<i8>();
+assert(i8Adder(127, 127) == -2);
+
+f1 = f2;
+assert(f1(4) == 4);