Make DetectionLayer return normalized coordinates
to avoid unnecessary conversion to pixels and back
to normalized.

Move code to separate functions and fix off-by-1
error.

Allows using a config variable, TRAIN_NB, rather
that updating the BatchNorm class.

skimage.transform.resize() crashes with a floating
point exception if the image has 1-pixel width or
height and the mode=“reflection”. Changing mode to
“constant” (the default) fixes the issue. And, 
it’s the correct mode to use anyway.

If the mask is a rectangle, its mini-mask pixels
become all 1s, and it has no zeros. Scipy imresize
fails on that and returns 0s instead. This update
fixes the problem.

Requires installing imgaug (pip3 install imgaug)
https://github.com/aleju/imgaug

List of augmentations:
http://imgaug.readthedocs.io/en/latest/source/augmenters.html

This is more reliable than using the batch size to
determine worker count because load per batch of 
images varies depending on image sizes and where
they’re loaded from.

Convert Detection Layer from Python to TensorFlow ops.

shapes more-or-less match now. weights load. current error=InvalidArgumentError (see above for traceback): WhereOp: Unhandled input dimensions: 0

Remove py_func for cross-environment serializability. Convert DetectionLayer/refine_detections to tf