Add return statement

tests/funcdefs.nct

@@ -2,6 +2,6 @@
 /* Oh and arguments aren't supported yet either */
 /* But functions work :) */
 
-u0() foo: u0() {
-	u8 a = 5;
+foo: u0() {
+	return 15;
 };

tests/mbr.nct

@@ -19,4 +19,4 @@ loop {}
 u8[19] string: "Hello from Nectar!\0";
 
 @align(510);
-u16 bootsig: 16rAA55;
+u16 bootsig: 16rAA55;