Release 2.3.1

This release provides the latest version for the second generation of pymzML.

Changelog (for details please refer to commit log)

• use black code style
• use tox for testing
• automatically deploy to pypi on tags
• update to newest plotly version
• add codecov bot
• add different badges to README
• add Contributing and Code of Conduct
• fix issue when averaging spectra (#147)
• add pull request template