Add Pillow

[hugovk]

Pillow will drop support for Python 2.7 on 2020-01-01. I'm a maintainer of Pillow, here's links to documentation and the relevant issues:

• https://pillow.readthedocs.io/en/stable/deprecations.html#python-2-7
• Drop support for Python 2 on January 1, 2020 python-pillow/Pillow#3642
• Document Python 2.7 will be dropped on 2020-01-01 python-pillow/Pillow#3682
• https://twitter.com/PythonPillow/status/1112944483253968896

Added above Scipy, as Pillow has 6,020 GitHub stars and Scipy has 5,620.

• https://github.com/python-pillow/Pillow
• https://github.com/scipy/scipy

[takluyver]

Thanks! I'll give any other core contributors (@radarhere?) a chance to confirm that they're happy for Pillow to be on the list.

[radarhere]

Sure - help spread the word that Python 2 Pillow users need to migrate.