Modified code to use OS independent header file for config settings.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

Remove extra spaces from mixers before processing them. This gives us some more working space on IO for mixer processing.

Make mixer ioctls load from a memory buffer rather than a file. This is prep for uploading the memory buffer to IO to be processed there.

Now the mixer is a C++ library that can be fairly easily bolted into an output driver to provide mixing services.

Teach the FMU driver how to use it as an example.  More testing is still required.

Solve the multiple publishers issue with 'control groups', one group per controller.  Mixer inputs now specify both group and control offset within the group.

Avoid using %f when loading/saving mixers; use scaled integers instead.