Invensense MPU-9250 SPI Library adapted for the use with Kalman Filter

https://github.com/TKJElectronics/KalmanFilter

Tested on Teensy 3.2

Does not use the built in DMP of the imu. Use this library only in combination with the Kalman Filter library (see example code), otherwise use the original one: https://github.com/brianc118/MPU9250