Bug fix & cleanup

- Found bug in update() function if payload size < 8 : it would not read the payload, but end up timing out or in a loop with the radio unuseable
- Re-order the code so the data always gets read from the radio and discarded if too small
- Remove 25ms loop/txTime variable for writes as the application should manage calling update & write
- Moved function declarations from cpp to h file
- Clean up some tabs to spaces in h and cpp file