add allow import circuits in circuits language compiler

circuitexamples/import-example.circuit

@@ -0,0 +1,8 @@
+import "imported-example.circuit"
+
+func main(private s0, public s1):
+	s3 = exp3(s0)
+	s4 = sum(s3, s0)
+	s5 = s4 + 5
+	equals(s1, s5)
+	out = 1 * 1

circuitexamples/imported-example.circuit

@@ -0,0 +1,7 @@
+func exp3(private a):
+	b = a * a
+	c = a * b
+	return c
+func sum(private a, private b):
+	c = a + b
+	return c