v1.0.6 add support for loading bgra32 format and fix save bug for alpha

there was a bug when the image could use a palette but also had an
alpha channel which meant the output image was invalid.

version 1.0.3

version 1.0.2

version 1.0.1

* use package icon and license expression settings for nuget package
* fix writing deflate stream content to be zlib compatible when creating png images
* add convenience methods for most common image creation use cases
* add convenience method to open png image from file path

add the unlicense, remove unused code and add documentation