Pure python PNG writer
Add @lcampagn 's make_png. No need to import from another library.
Just `from vispy.util import make_png`
No need the alpha toggle in make_png
- Dimension can be obtained by data.shape[2]
- Check for dimension and data type
- Add alpha toggle to _screenshot
Improve readability
Flakify
Update docstrings, add more information.
Update docstrings for screenshot and read_pixels
Add test for make_png
Save random RGBA and RGB arrays onto disk as PNGs using `make_png()`.
Read them back with an image library and check whether the array saved
is equal to the array read.
Refactor code to import same decorator
Add `requires_img_lib` decorator and use it in test_image and test_dataio.
Update test_image to reduce redundancies.
Merge pull request #303 from mfkaptan/make-png

Pure python PNG writer