added support for function imports

xorscroll.cwa

@@ -0,0 +1,9 @@
+import "env.memory" memory(2);
+
+export fn tic(time: i32) {
+  let i: i32;
+  loop frame {
+    i?120 = (i % 320 + time / 10) ^ (i / 320);
+    branch_if (i := i + 1) < 320*256: frame;
+  }
+}