refactor

[plusk01]

This PR breaks the existing API in favor of various simplifications, fixes, and code clean ups.

• put register address definitions into separate private file
• setAccelFS and setGyroFS do not clobber entire register anymore (previously would override ODR setting)
• added public setAccelODR and setGyroODR functions
• Fixed enableDataReadyInterrupt and tested
• removed readAccel and readAccelGyro and renamed readSensor to getAGT for simplicity (mirrors SparkFun's ICM 20948 library)
• simplified data access API to accX(), ..., gyrZ(), temp() to mirror SparkFun's lib
• removed hardcoded rotation matrix
• removed unit conversions -- data is now in g's and dps --> this and previous change forces the user to deal with these details
• fixed temperature scale and offset constants according to the datasheet (Section 4.13)
• added inline documentation in ICM42688.h
• updated examples and cleaned up README documentation
• allow user to set SPI_HS_CLK (since ICM42688 supports up to 24 MHz) --> defaults to 8 MHz

tested with SPI on esp32. FIFO code remains to be reviewed and tested.

[plusk01]

after i test that everything is working well in a larger project, i'll merge and create a new tag (v1.1.0) to update the arduino library register