Kwimage

Added
* thickness to `Boxes.draw_on`
* add `.round` to Boxes, Points, and Coords
* add `Boxes.contains`
* add `kwiamge.load_image_shape`
* add `MultiPolygon.fill`
* `kwimage.imwrite` now accepts the `backend` keyword, which can be `cv2`, `skimage`, or `gdal`. The `gdal` backend writes images as cloud-optimized-geotiffs.
* add `kwimage.structs.Segmentation` which encapsulates Masks, Polygons, and MultiPolygons
* Add `im_filter` which currently contains fourier domain filters.

Fixed:
* issue with `draw_clf_on_image` when truth is unknown

Fixed:
* fixed issue where non-max-suppression couldn't find a default implementation.

Changed:
* Faster color casting

Fixed:
* Misc coco fixes.

Added
* Tentative `Color._forimage` method

Changed
* Simpler demo data file names.
* The kwimage.struct `draw_on` methods now operate in-place (more often) when possible.

Fixed
* Fixed color in kwimage.struct `draw_on` methods.
* Detections concatenate now works when segmentations are populated.

Added
* `imresize` now accepts `letterbox` flag.
* add `numpy` and `tensor` methods to `Mask`

Changed
* `ensure_alpha_channel` now accepts `dtype` and `copy` kwargs.
* `Mask.draw_on` will now draw on images larger or smaller than the mask itself


Fixed
* Fixed Boxes.draw
* `Boxes.draw_on` now works correctly on uint8 and float32 images with 1, 3, or 4 channels
* `Masks.draw_on` now works correctly uint8 or float32 images
* Fixed error in `draw_clf_on_images`
* Fixed scale error in `Detections.random` when `segmentations=True`