missing debounce for rx pin

Hi 
Nice library.
However decoder is not working properly when inout is noisy
I have added a debounce in checkIncoming routine

```.c
void Lewis::checkIncoming()
{
  uint32_t current_time = millis();
  static uint8_t current_state;
  static float average = 0.;
   
  average = 0.01*digitalRead(_rx_pin) + 0.99*average;
  current_state = floor(average +.5);
  ...
```
  