add functions to convert containers directly into packet

src/packet.rs

@@ -108,6 +108,9 @@ pub unsafe extern "C" fn sp_packet_free(packet: NonNull<Packet>) {
     unsafe { heap_drop(packet) }
 }
 
+/// Converts u16 into [CommandCode].
+///
+/// If the provided value is not valid, false is returned and result is not changed.
 #[no_mangle]
 pub unsafe extern "C" fn sp_u16_to_command_code(
     code: u16,