v2.4.0

Upgraded CNER system

• Rewrote the BERT CNER tagger using native transformers and torch; removed the dependency on the archived allennlp pacakge.
• Updated the requirements for installing ChemDataExtractor2

Python Versions

• Dropped the support for Python 2
• Updated the requirements so that ChemDataExtractor2 runs on Python 3.9 or higher.

Code Formatting

• Formatted the .py files using Black