Updates subpixel API and warning fixes (#268)

* Homogenize the subpixel API and fix/suppress warnings in tests

* Fixes subpixel for edge case where FFT is 0

* Weird init issue causing tests to fail?

* missed a debugging print

* Fixes dtype in ring_matcher dynamic growth

* Thanks @Kelvinrr debug print

* Fixes for networkx 2.3 improvements to subclassing

* Travis precision differs from macbook

* typo

* typo