Library for teensy 3.x quadrature decoders

So for a class project I wrote a class to use the the Teensy 3.1 hardware decoders. I was inspired by tlb https://forum.pjrc.com/threads/26803-Hardware-Quadrature-Code-for-Teensy-3-x but wanted to write it up so I understood the hardware. I then had a friend help me write it in a template class form and now i've maid it into an actual Arduino library. currently there is an issue and I can only use one set of pins for the FTM1 (pins 16/17), I'm not sure why the other set doesn't work (pins 3/4). The example I wrote up use the Pololu's dual MC33926 motor driver shield https://www.pololu.com/product/2503 and one of there 25D mm geared motors https://www.pololu.com/product/2285. I'm posting this for two reasons, the first is so that other people can use it if they so desire. The other is in hopes to get some feedback on this library. It's the first time I've written something like this as a library (I created a wrapper library for the SSC-32u but that wasn't nearly as complex), and would appreciate any constructive criticism.