Kwimage

Added:
* Working on QOI support
* Added `kitware_green` and `kitware_blue` "Kitware colors" in `kwimage.Color`.
* Type annotations stubs


Changed:

* Moved binary backends to `kwimage_ext` module as optional dependencies. Kwimage is now a pure python package.

Added:
* Intention: ndarray functions in kwimage and kwarray should respect masked arrays.

Changed:
* Deprecate using overview=-1 to get the coarsest overview. Use the string "coarsest" instead.
* The "overview" argument to gdal now uses 0-based indexing such that overview=0 is no overview,
and overview=1 is the first overview. This corresponds to the scale being `2^{overview}`.

Added:
* `kwimage.Affine.to_shapely` method for converting affine transforms to shapely-style

Fixed
* Fix issue in `Polygon.draw` where facecolor and edgecolor were not respected.
* Added `to_shapely` for `kwimage.Affine`
* Issue in `kwimage.load_image_shape` when using pathlib.Path

Fixed
* Bug in `Detections.draw_on(..., color='classes')` when a class is unknown
* Added workaround to cv2 bug to `Polygon.draw_on` when polygon coordinates are
too large. Currently clips the polygon and emits a warning, this prevents
crashes, but results may not be correct.


Changed
* `Boxes.from_slice` no longer handles wraparound slices as it is not well
defined and previous behavior was buggy.

Added
* facecolor and edgecolor in `Polygon.draw_on`

Fixed
* Bug in MultiPolygon draw, `Polygon.draw_on` no longer crashes when polygon is empty.
* imread overviews now work for grayscale images

Changed
* Speed up drawing in PolygonList and other generic draw funcs
* improve checkerboard

Added
* Added option to mask nodata regions when using imread and gdal backend.
* Added area property to Polygon and MultiPolygon.