compiler: add complex manipulation

* builtins: real, imag, complex
* printing of complex numbers

No support for complex arithmetic yet.

testdata/float.go

@@ -23,4 +23,24 @@ func main() {
 	// casting
 	println(float32(f64))
 	println(float64(f32))
+
+	// complex64
+	c64 := complex(f32, 1.2)
+	println(c64)
+	println(real(c64))
+	println(imag(c64))
+
+	// complex128
+	c128 := complex(f64, -2.0)
+	println(c128)
+	println(real(c128))
+	println(imag(c128))
+
+	// untyped complex
+	println(2 + 1i)
+	println(complex(2, -2))
+
+	// cast complex
+	println(complex64(c128))
+	println(complex128(c64))
 }