#15 #14 Improve fragmentation and transfer speed

Notes:
- May require updating the RF24 driver (radio.rxFifoFull())

- Continue buffering data if a Network Ack is received and there is data
in the FIFO
- Fragmented payload handling improvements
- Repair and tested non-fragmented and fragmented data transfers with
user-defined header types
- Handling for data sent to self
- Stop listening during fragmented data transfers, speeds up data rates
(more to come)
- Adjusted frag_delay.
- Thanks to https://github.com/reixd and rRF24toTUN for making testing
things a lot easier