Implemented loop iterators

tests/programs/index-static.q

@@ -0,0 +1,20 @@
+import mem
+
+main() {
+	a := mem.alloc(4)
+
+	assert a[0] == 0
+	assert a[1] == 0
+	assert a[2] == 0
+	assert a[3] == 0
+
+	a[0] = 0
+	a[1] = 1
+	a[2] = 2
+	a[3] = 3
+
+	assert a[0] == 0
+	assert a[1] == 1
+	assert a[2] == 2
+	assert a[3] == 3
+}