[Library Manager] add DualVNH5019MotorShieldMod3

[photodude]

Please consider adding https://github.com/photodude/DualVNH5019MotorShieldMod3 to the library manager index

This is a custom library for the Arduino that interfaces with two Pololu Dual VNH5019 Motor Driver Shields with an Arduino Mega. It makes it simple to drive four brushed, DC motors from 2 shields on an Arduino Mega.

This is a modification of the pololu library pololu/dual-vnh5019-motor-shield extending the functions to work with two shields and 4 motors on an arduino mega. The library is referenced in on the Pololu resource page https://www.pololu.com/product/2507/resources

[cmaglie]

Done!

[photodude]

@cmaglie thank you.