ArduPPM: Sorry forgot to push version number of PPM Encoder for ATMEGA328p
README: rewritten to be up to date
Remove README_AP_HAL, which is woefully out of date
Correct spelling of run_navigation_contollers
DataFlash: move log reading logic into common library
Copter: use common log reading function
Plane: use common log reading function
Rover: use common log reading function
Copter: constrain auto roll and pitch to 45 degrees
Copter: update firmware version to rc5
Copter: bug fix to altitude check of verify takeoff

set_next_WP function was not setting the alt_change_flag properly
Copter: RTL bug fix to initial step is always a climb and not a descent

Also bug fix to hold yaw on take-off
Filter: added 2nd-order butterworth filters.
autotest: tweaks to Rascal tuning
Butter filter: needs header guards
AP_HAL: added AP_HAL_Macros.h

this adds a define for constexpr, allowing code to build either with
or without -std=gnu++0x
Filter: fixed butter filter build on px4
Filter: added a butter filter to example
Update floating point calculations to use floats instead of doubles.

- Allows use of hardware floating point on the Cortex-M4.
- Added "f" suffix to floating point literals.
- Call floating point versions of stdlib math functions.
Add AVR compatibility header for missing math.h definitions.

- Define float versions of math functions to the double versions
  on AVR (eg. #define sinf sin).
- These macros appear to be missing in older versions of avr-libs.
- Include AP_Math.h rather than math.h to get these definitions.