v0.4.19

What's Changed

• migrate from setup.py to pyproject.toml by @njzjz in #265
• document different contexts and batches by @njzjz in #266
• Fix typo in pr#266 by @HuangJiameng in #267
• Change Lebesgue API Service To Bohrium API Service by @KZHIWEI in #268
• drop Python 3.6 support by @njzjz in #270
• support machine and context alias by @njzjz in #269

Full Changelog: v0.4.18...v0.4.19