Reduce serial port memory usage.

The largest MSP command is 160 bytes.
Updating CC3D docs.
Update RC Controls so that functions with different modes can be
applied.  The existing modes are 'step'.  A new mode is 'select'.

The other unit tests need fixing up so that appropriate code is compiled
as C and not C++ code.
Add rate profiles and inflight switching between them.  See Profiles and
Inflight Adjustment documentation for details.
Add Profile OLED display page that shows the current profile and rate
profile.
Rename default_rateProfile_index to defaultRateProfileIndex.