First cut of allowing a 3POS switch on AUX3 to change rc rate.

rcRate is decreased when low, increased when HIGH and no change when the
switch is in the middle.

The rcRate ticks up/down at 0.01 every 500ms if the switch is left on.

If using a momentary switch and if you can toggle the switch between
middle and low or middle and high more frequently than 500ms then the
rate will be increased accordingly.  Similar to how a keyboard repeat
behaves.
Make the adjustment controls more sensitive by using a smaller 3POS
switch deadzone.
Fix rc_controls_unittest to use midrc.
Update adjustmentConfig to include the adjustment timeout.
Use adjustment index rather than function to track state.
Seperate adjustment configuration from adjustment state.  Rename 'step'
parameter to 'delta' applying the adjustment.  Configure adjustment
states based on adjustment configuration for AUX3 and AUX4.
First cut of API documentation.

Note this is already out of date for current master branch.
update some comment typos in sensors/acceleration.c
Beep when adjustments are made. (very short = adjust downwards, short =
adjust upwards).
Extract range definition so it can be reused.
Add cli command to configure adjustment ranges.

e.g. `adjrange 0 0 1700 2100 1 2`

set adjustment range 0, which applies to aux channel 0 (aux1) when range
is between 1700 and 2100 then apply function 1 (rc rate) to aux channel
2 (aux3)
Update `adjrange` command to take an 'adjustment index/slot'.  Apply
adjustment ranges to adjustment slots when channel is within range.

example:

```
adjrange 0 0 0 900 1700 0 2
adjrange 1 0 0 1700 2100 1 2
```

explained:

* configure adjrange 0 to use adjustment slot 1 (0) so that when aux1
(0) in the range 900-1700 then do nothing when aux 3 (2) is in any
position.
* configure adjrange 1 to use adjustment slot 1 (0) so that when aux1
(0) in the range 1700-2100 then do use adjustment 1 (rc rate) when aux 3
(2) is in the appropriate position.

Without the entire range of aux1 being defined there is nothing that
would stop aux 3 adjusting the rc rate once aux 1 wasn't in the higher
range. 

There are 4 adjustment slots and 12 adjustment ranges.

Adjustment slots and adjustment ranges can use the same aux channel.

e.g.

`adjrange 2 1 0 900 2100 1 3`

* configure adjrange 2 to use adjustment slot 2 (1) so that when aux4
(3) in the range 900-2100 then use adjustment 1 (rc rate) when aux 4 (3)
is in the appropriate position.
reorder aux/adjrange commands, commands must be alphabetically sorted
due to the command-lookup code.
Allow inflight adjustment of pitch/roll rate.
Allow inflight adjustment of rc_expo.
Allow inflight adjustment of yaw rate.
Allow inflight adjustment of throttle expo.
Avoid warning when target does not use beeper.
Allow saving of config when disarmed by using THR_LO + YAW_LO + PIT_LO +
ROL_HI.
Allow inflight adjustment of pitch/roll (linked) and yaw PID settings.