General cleanup based on the pull request from muggenhor
Reformatting.
First steps to supporting GPS
More changes.
Merge remote-tracking branch 'upstream/master' into hott_v2
Add some GPS data to telemetry message.
GPS support - mostly working.
Merged new repository layout from PX4/Firmware
Initial work of so3 nonlinear complementary filter
I missed to add build command
Fixed few minor bug
I do not know why roll angle is not correct. But system looks okay
Roll pitch yaw should be verified again
To use freeIMU processing visualization tool, I have implemented float number transmission over uart (default /dev/ttyS2, 115200)
But this not tested yet. I should.
Test flight has been performed with nonlinear SO(3) attitude estimator.
Here are few observations:
 - When the system initialized, roll angle is initially reversed.
   As filter converged, it becomes normal.
 - I put a negative sign on roll, yaw. It should naturally has right
   sign, but I do not know why for now. Let me investigate again.
 - Gain : I do not know what gain is good for quadrotor flight.
   Let me take a look Ardupilot gain in the later.

Anyway, you can fly with this attitude estimator.
sdlog2 logger app added. New flexible log format, compatible with APM.
sdlog2 strick packing fixed, length bug fixed, "sdlog2_dump.py" debug tool added
sdlog2_dump.py now supports all fileds formats and able to parse original APM log
sdlog2_dump.py now generates customizible CSV output, messages/fields filter added.
sdlog2_dump.py now dumps CSV columns in the same order as args