This makes failsafe much easier to configure on the flight controller.
The previous behavior of setting all the channels to 1000 was a bit
confusing because the pulses my flight control was receiving were
already less than 1000, so going into failsafe actually raised all
channel levels until I adjusted subtrim on throttle to keep it around
1010.

With this code, it simply stops pulsing in such a way that matches what
the frsky d4r does (see below).  This is a well-known and unambiguous
path.

D4R losing radio contact:  http://i.imgur.com/8Xd27VQ.png

This code losing radio contact: http://i.imgur.com/lxGL4CT.png

Use a fixed RSSI percentage range.

Based on a bit of sciencing around what I thought would be good range, I
came up with some values to constrain "0-100%" with for translation to
ppm values.

http://i.imgur.com/X42wxL1.png

Auto binding when uninitialized and RSSI over PPM

The onState is backwards.