Kwimage

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.

Added

* Added option to `ignore_color_table` when using gdal imread backend.

Changes

* Fixes for `intensity_normalize`
* Allow user to specify nodata, transform, and crs when writing a geotiff


Changed
* Consolidated environment variables in a new `kwiamge._internal` module.

Fixed
* Previously Polygon.fill would only fill the first channel, this is now fixed
* `kwimage.imwrite` now raises an exception if the file fails to write.
* Fixed alpha in `Polygon.draw_on` for polygon borders.
* Fixed issue in `load_image_shape` when PIL fails.

Added

* `kwimage.Color.distinct` now uses `distinctipy` as a backend, and gains
functionality to exclude existing colors.


Fixed

* Serious bug in `kwimage.Affine`, where `decompose` and `affine` were not
inverse. Behavior of kwimage.Affine with shear is now deprecated as it was
inconsistent. New parameter that impacts shear is `xshear`.

Changed
* Mask translation is now more efficient for c/f formats.

Fixed
* Bug introduced in `Mask.to_multipolygon` which caused bad offsets

Added:

* `pixels_are` flag to `to_mask` / `to_multi_polygon` methods, which can be
points or areas. The latter uses a rasterio contour finding mechanism.
* `imread` gdalbackend can now read from overviews if they exist.

Fixed:
* `warp_affine` now properly raises an error when cv2.warpAffine raises an unhandled error
* Polygon to/from methods now handle the empty polygon case

Changed
* Improved polygon / segmentation coercion methods