Broken out SPI bus configuratino to its own method. SPI access is not
prefixed with this new private method to ensure proper operation when
multiple SPI devices are in use.
Hopefully fix a radio write bug.
Changed SIP bus speed to use a divider of 4 for enhanced
compatibility.
Merge branch 'master' of https://github.com/maniacbug/RF24
Merge clean up.
Added some additional debug options (commented out) for testing. More
merge cleanup (printDetails).
Yet more merge cleanup. Changes default channel to be
US/Internationally legal while ensuring no spectrum bleed.
Performance optimizations. Radio no longer automatically powers down.
Radio is now allowed to enter standby. This allows for the removal of
needless delays within the driver. Additional timings optimizations.
If applications desire additional power savings, they should manually
power down the radio as needed.

Multicast write support added.

::write timeout monitoring logic changed to emcompass worst timeouts
for retries/timeouts. Should never trigger anyways...but better safe.

Fixes write retries timeout bug.

Proper hardware delay added to powerUp. Was previously part of
startWrite; which needlessly added overhead to every write/startWrite.

Allows for query of hardware channel.

PA documentation fixes.
Previous commit message applies here.
Fixed write hardware timeout monitoring. Timeout is now dynamically
calculated based on current hardware configuration. There is room
for optimization via caching.
Fixed spelling.
Changed timeout calculation from ms to us as usual math resulted in
loss of resolution and the possibility of a premature timeout. The
write monitoring loop now uses us rather than ms to be more compatible
with the us result returned from getMaxTimeout.
Normalized write and startWrite interfaces for multicast. Now both take
a bool for multicasting. Documentation updates.
Updated documentation for multicast warnings.
More doc updates.
Minor cleanup. Documentation change for multicast.
Docs.
Example changes. Pingpair now reports a more accurate round drip without
artificial delay. Examples use more options. Added a new multicast
examples based on pingpair_dyn; pingpair_multi_dyn.
Removed redundant headers as its already included, and required, by
RF24.h. Fixed some radio power up/down issues in code which relied
on side effect behavior of radio powering down after every TX.
Applications now take responsibility for power management.
Removed redundant arduino < 100 header include.