Implemented multiple return values

tests/programs/return-multi.q

@@ -0,0 +1,28 @@
+main() {
+	a, b := reverse2(1, 2)
+	assert a == 2
+	assert b == 1
+
+	c, d, e := reverse3(1, 2, 3)
+	assert c == 3
+	assert d == 2
+	assert e == 1
+
+	f, g, h, i := mix4(1, 2, 3, 4)
+	assert f == 4 + 1
+	assert g == 3 + 2
+	assert h == 2 + 3
+	assert i == 1 + 4
+}
+
+reverse2(a, b) {
+	return b, a
+}
+
+reverse3(a, b, c) {
+	return c, b, a
+}
+
+mix4(a, b, c, d) {
+	return d + a, c + b, b + c, a + d
+}