* Fixes bug in imgaug.Hue

Hue range of cv2.cvtColor() is 0-360 for floating point images (and 0-180 for 8-bit images), see
https://docs.opencv.org/3.2.0/de/d25/imgproc_color_conversions.html#color_convert_rgb_hsv.

* fix lint

* add link about opencv hue range

* add enhancenet

* fix liniting

* another battle against Python3 linter

* fix gram matrix

* follow suggestions

* fix suggestions

* add teaser again

* small docs & style fix

* simplify VGG mean

* small changes

* switch to space_to_batch