Implementation of the PX4 flow algorithm for ardupilot.
Based on the original PX4 Flow code, it has diverged a lot.
I have kept the license header since it is required.
I have removed all the unused and dead code on current implementation,
modified the code to make it clearer, re-indented it and changed
the way some params are calculated. It has been tested on PC and
on board and showed results that I assumed were OK. No optical flow
Loiter tests have been undertaken since it requires a Sonar which will
be added soon.
Limitations :
Some parts were written in ARM assembly and I rewrote them very naively
to get them to be more easily portable. A simple optimisation would be
to re-introduce assembly code for ARM as a separate asm file with
methods for fixed resolutions that would reduce a lot the amount of
calculation and memory read/writes. Then writing a version in NEON
assembly would even be more optimised and then maybe an Intel version.