Add calibration function to support measuring highest current resolution possible (0.1mA) at lowest range (16V, 400mA).

Here's a convenience function to configure the INA219 calibration to support measuring at 0.1mA resolution of current at 16V, 400mA max.  The function is not used by default because the range is much lower than the current default of 32V at 2A, instead it's provided as a convenience for anyone that doesn't want to calculate the values themselves.

Tested this by measuring the same load (an Arduino running a sketch consuming ~30mA up to ~140mA at specific points) and confirming this calibration had better current milliamp resolution.