Added support for encoding and decoding iTXt chunks.
Added iTXt tests.
Added tests for iTXt saving.
Save detected non-Latin1 characters as iTXt to preserve them.
Test unicode preservation in text chunks.
Merge pull request #818 from dolda2000/itxt

Added support for encoding and decoding iTXt chunks.
Update CHANGES.rst [CI skip]
Image Mode Docs
Merge pull request #825 from wiredfool/hsv

Image Mode Docs
Add CONTRIBUTING.md [CI skip]
Merge pull request #826 from hugovk/CONTRIBUTING

Add CONTRIBUTING file
Merge branch 'master' of https://github.com/python-pillow/Pillow