v3.1.0

• Added compatibility checker to give more information when
  interpolable builds fail. Automatically enabled for variable font
  or optionally for interpolated static instances when the
  --check-compatibility flag is passed (#832).
• Bumped minimum requirements (incl. various bugfixes):
  • fonttools >= 4.28.5
  • glyphsLib >= 6.0.1
  • ufo2ft >= 2.25.2
  • ufoLib2 >= 0.13.0