Merge pull request #1 from zephyrr/master

Merge improved write_payload() and read_payload()  - looks good and passes my testing.
ATTiny support fr jscrane fork tested and working

ATTiny support pulled in from https://github.com/jscrane/RF24
- SPI support for ATTiny is included with the library. Do NOT include
SPI.h with tiny.

Pin info etc can be found at:
http://programmablehardware.blogspot.ca/2013/09/rf24-with-attiny84.html

ATTiny 85 Example:
RF24 radio(4,3);    // CE: 4  CS: 3
enableDynamicAck(), Single NOACK, default RT,

- Added new function: enableDynamicAck()  to enable single-write NOACK
payloads (merge closer with gcopeland fork)
- Added single NOACK writes for write(), writeFast(), startWrite() and
startFastWrite()
- powerUp() now checks to see if radio is powered on. No delay if
powered up.
- radio must still be powered up manually if powered down manually
- use setRetries function in begin()
- set CE low on powerDown
- updated readme
Revert powerUp() delay to 5ms delay

For nRF24L01+ to go from power down mode to TX or RX mode it must first
pass through stand-by mode.
There must be a delay of Tpd2stby (see Table 16.) after the nRF24L01+
leaves power down mode before
the CEis set high.

5ms is the maximum defined in the v1.0 datasheet
Fix: Return value of write, writefast
Update examples, minimize code size

- Updated some example files and tests
- Small changes to minimize code size
FIFO rd change (Thanks Zephyrr), Initial SI24R1 support

- Using status register is faster to read TX FIFO status - Zephyrr (GitHub)
- Fixed typo on FLUSH_RX cmd
- Added support for pwr levels on SI24R1 chips with smaller code
Small fix before pushing last commit

- fixed mistake with changes to setPALevel prior to pushing
Raspberry Pi support

Added support for hardware SPI on RPI per jscrane fork:
- Fixed a few bugs with single SPI transfers
- Aligned with optimized RF24 library fork
- Updated bmc2835 files per
http://www.airspayce.com/mikem/bcm2835/index.html
- Merged bcm files with changes from
https://github.com/farconada/RF24Network
- Added example files
- Added setup info to readme
fix typo in readme
RPi SPI functionality and RPi fix for startWrite

- Enabled use of hardware CS1 pin
- Removed custom_cs code for software driven CSN
- Modified BCM driver to allow use of hardware SPI pins not in use while
SPI is active.
- Updated constructor in examples
Install header files and separate install task
Bring readme.md inline with new Makefile
Cleanup readme syntax
Cleanup table in readme
Use spaces, not tabs, in readme.md
make install should build first
Restore closeReadingPipe

Restore closeReadingPipe to be compatible with mysensors
Merge pull request #4 from a-lurker/master

Restore closeReadingPipe merge for mysensors
Merge pull request #2 from cornet/fix-rpi-build-scripts

Makefile fixes