Reliability improvements for RPi

- In testing with python wrapper, found setting CE(HIGH) sooner in
startListening() prevents issues
- Changed delay between available() checking on RPi to prevent what
seems like saturation of the RF24 module with SPI requests
- Reduces errors when switching between RX/TX modes
Remove unnecessary delay

Further testing indicates this is not needed
Revert last commit, if defined... delay

Delay is necessary for faster devices in some cases
- reduced delay by 30us for testing further
Merge pull request #35 from mz-fuzzy/master

Python wrapper for RPi added

This wrapper and the pingpair_dyn example seems to have brought up a bit of a timing issue that should be fixed in the latest commit https://github.com/TMRh20/RF24/commit/d41d47ab20cb794b8250560154076b1b2b06feae  
Also, (minor issue) it seems to be missing the define for ```BCM2835_SPI_CS0``` and ```BCM2835_SPI_CS1``` 
That can be fixed, and it seems to work nicely otherwise, so merging.
Revert change to delay from last commit

Further testing after including python wrapper indicates the original
delay seems to be about this best its going to get as far as a
compromise between delaying a bit/throughput and reliability of payloads
when rapidly switching between modes.