allow controlling external XOR gate connected to PB2 (BOOT1) to invert USART2_RX signal on F1. Currently used by sbus driver.
On second thought, no need to make inverter configurable. only sbus will use it, and the driver can set inversion automatically.
Fixing gimbal_flags not working when feature SERVO_TILT was enabled. This was done by properly calculating servo offset instead of depending on enabled features/mixers.
remove unnecessary variable
unroll loop for better code size

gcc remove 29 bytes here
Merge pull request #122 from treymarc/patch-7

remove unnecessary variable
Merge pull request #123 from treymarc/patch-9

unroll loop for better code size
remove unnecessary variable. unroll loop for better code size.
Merge remote-tracking branch 'multiwii/master'
Renamed alt_hold_throttle_neutral to alt_hold_deadband for consistency.
Shorten warning beeps.
Cleanup mismatch of buzzer/beeper terminology.  Beep and Beeper should
be used from now on.
Extract Altitude Hold code from mw main loop into methods.
Move altitude hold code into separate files.
Move mw loop() code into separate methods.  Cleanup related code.

If a given feature or mode is off the next task is not processed in the
current loop but will be processed during the next loop iteration for
simplification, this allowed the cleanup of return values in other code.
Disable ADC debug output and enable AltHold debugging output.
Prevent bad data being used during early system startup.
Some baro cleanups to avoid using or exposing incomplete and
uninitialised baro data.

imu code size reduction (treym)
Explicitly use float literals in velocity calculation.
Fixing missed multiwii scale factor accidentally removed from
432c43bab7e76f2d6ef66bd9cc8edf9289fbdae8 during merge.