Change the way modules are built so that object paths are relative and use vpath for locating sources (so source paths are also shorter).

Add some basic documentation for the build system files while we're at it.

Marko Pagott <p0rc0.jet@gmail.com>

Quad wide arm mixer

MD25 Motor Controller Driver

Hil press fix

Velocity based gain adjustment based on dynamic presssure

Update servo arm only on real change.

Accelerometer calibration bugfix

6point accel calibration

Still threshold increased to 0.1m/s^2, and orientation error threshold to 5m/s^2. Timeout increased to 30s.

mkblctrl: some small fixes