Merge RPi and Arduino code

Merged code to simplify everything
- #31 Timing of stopListening() adjusted slightly to further prevent
blank ack-payloads if powering down while using ack-payloads or
switching between modes
Fix for last commit (code merge)

Prevent inclusion of BCM2835 driver for non-linux devices
Replace old examples with the current ones for RPi

Accidentally copied old RPi examples on last commit (code merge)
Moved RPi SPI driver to RPi folder from root

- Moved bcm2835.h and .c to RPi folder
- Changed includes and makefile to accommodate
Incr delay in stopListening(); Fix transfer example

- Testing with Arduino & RPi indicates delay needs to be increased
slightly before flushing tx_fifo
- Fix addresses in RPi transfer example, and add stopListening()
Fix include for RF24_config.h