sopel-twitter 1.4.0

Changed:

• Updated tweety-ns library to 2.x (#70)
• Require Sopel 8
• Require Python 3.9+; tweety's code raises errors on 3.8 even though Sopel 8
  still supports it

Meta:

• Updated packaging & upload workflow
• Cleaned up unused imports & Python 2 era cruft
• Updated plugin file header (licensing)
• Reformatted changelog with cleaner headings and an actual entry for 0.1.0