Improve gen_dense_coords to allow for reuse during prediction time
Improve gen_dense_coords to allow for reuse during prediction time

This updates `gen_dense_coords` to include coordinates for patches with
padding along the left and top edges.  With appropriate striding, the
right and bottom edges can also be included.

Closes #13.

dusenberrymw/deep-histopath,dusenberrymw/deep-histopath