(First draft) Added functions for reading/writing registers and conve…

[bjackson312006]

Changes

• Created INA226.c and INA226.h

• Wrote functions for reading and writing to registers, setting up the calibration register, setting up the configuration register, and converting current, power, and voltage into real values

To Do

• Stuff w/ the alert register and the mask/enable register
• Possibly individual functions for configuration settings
• Corrections to the code I've already written
• Remove some comments when done
• Store current_lsb as an int and possibly change other data types

Resolves #152

[jr1221]

Please add the public functions to the .h file. This allows the application using the driver to call the functions in the code.