deshima-dev/decode: Update release

Important notes

• The support of Python 3.6 is dropped from this version.

• Require init.py in sub-packages by @Hoshock in https://github.com/deshima-dev/decode/pull/20
• Update development environment by @astropenguin in https://github.com/deshima-dev/decode/pull/27
• Update supported Python versions by @astropenguin in https://github.com/deshima-dev/decode/pull/29
• Release v0.6.0 by @astropenguin in https://github.com/deshima-dev/decode/pull/31

• @Hoshock made their first contribution in https://github.com/deshima-dev/decode/pull/20

Full Changelog: https://github.com/deshima-dev/decode/compare/v0.5.9...v0.6.0