Add LiPo fuel gauge

[jeff-winn]

As a user, I need to know when the blaster is close to running out of power.

This will need to support two independent features:

• Kill switch (shuts down the blaster motors)
• GATT characteristic for battery level

Also, this must support 3S along with 2S LiPo (optional).

[jeff-winn]

Here's an example fuel gauge using the MAX17043G+U IC from Maxim Integrated:
https://www.sparkfun.com/products/10617

Datasheet for the above mentioned IC:
https://datasheets.maximintegrated.com/en/ds/MAX17043-MAX17044.pdf

GitHub project for an example:
https://github.com/sparkfun/SparkFun_MAX17043_Particle_Library

GitHub project for the breakout board:
https://github.com/sparkfun/Lipo_Fuel_Gauge