examples/sensor_fusion: Support for Madgwick Fusion lib and example

[fdcavalcanti]

Summary

This PR adds support for the Madgwick Algorithm (Sensor Fusion Library) and adds an example that uses this lib with the MPU6050.
The library is under Application Configuration -> Inertial Libraries Support and requires MIT licenses to be enabled.
The example is available under Application Configuration -> Examples -> Sensor Fusion Example.

On compilation, it downloads the Fusion library from Github and the header files can be accessed using:
#include "Fusion/Fusion.h""

Next PRs should add board example and the example code will support other IMUs.

Shout out to @acassis for helping to set up the library entries!

Impact

New entry on Application Configuration and new example is available. This can be useful for those who use NuttX to control drones.

Testing

Testing works fine using MPU6050 on a Tiva-C development board.
I need some assistance on linter issues. Not sure how to solve the following error due to the Fusion library naming convention:

root@DESKTOP-G6CVIMP:~/nuttxspace/nuttx# ./tools/checkpatch.sh -f ../nuttx-apps/examples/sensor_fusion/sensor_fusion_main.c
/root/nuttxspace/nuttx-apps/examples/sensor_fusion/sensor_fusion_main.c:78:2: error: Mixed case identifier found

On sensor_fusion_main.c

  FusionAhrs ahrs;
  FusionAhrsInitialise(&ahrs);

Any ideas on how to fix this?

[xiaoxiang781216]

@fdcavalcanti Mixed case could be ignored for the 3rd party library. But please fix other ci issue.

[fdcavalcanti]

Thanks for the code review!
All issues addressed. Only the mixed case issue on 3rd party library remains.

[fdcavalcanti]

Thanks again for the review @xiaoxiang781216
It would be great if someone could validate this using the MPU6050. I'm getting some bad readings on mine, I believe it might be on its last legs..

[xiaoxiang781216]

please add Kconfig to the .gitignore like other similar folder to fix the following warning:

HEAD detached at pull/2113/merge
Untracked files:
	inertial/Kconfig

[fdcavalcanti]

Gitignore added.