ManualControl: apply expo to all rate type modes

The rate expo term can be applied to weak leveling, axis lock, and
relayrate modes.  This moves the math to a macro and does that.
ManualCommand: move expo terms to one line

This is a really ugly long line, but makes the overall code
probably more readable.
Expo: fix expo macro calculations

Scaled previously before exponential.  This ruined the max
and min calculations.  Also the expo approximation equation
was wrong.
Expo: make it a function instead of macro
Merge pull request #950 from TauLabs/expo_ratemodes

Expo ratemodes