GitLab

* Add encode/write_png functions

* Do not redefine

* Style issues correction

* Comply with low-level interface

* Minor comment correction

* Add python frontend functions

* Add encode_png test

* Pass compession level to encode_png

* Do not compare output buffers

* Convert to bytes

* Compare pil image instead of buffer

* Add error tests

* Add test_write_png

* Remove png test assets

* Register writePNG correctly

* Update write_png docstring

* Do not preserve PIL image beyond the scope
Co-authored-by: Francisco Massa <fvsmassa@gmail.com>