Kwimage

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

Added
* kwimage.morphology
* kwimage.draw_header_text
* `Mask.to_multi_polygon` and `Polygon.to_mask` now take a flag `pixels_are`
which will treat pixels as areas or points.


Fixed
* But in imresize when a dim was automatically computed to be zero.

Changed
* Using `math` is much faster than `numpy` for scalars, switching to that in kwimage.Affine
* Added default behavior to `draw_text_on_image` when origin is unspecified.
* Polygon and MultiPolygon coerce work better with geojson
* Work on new robust normalizers (see `normalize_intensity`)