v1.4.0

• Don't remove overlaps from empty or all-component glyphs, or else pyclipper fails with an error (27d7b4c, #389).
• Remove pre-existing instance UFOs before calling MutatorMath (6cdf44e, #372).
• Do not round geometry in interpolated instance UFOs. Added a new option --round-instances to re-enable old behavior (#390).
• Use font.path attribute if present to generate the output path (#357).
• Support building varfont from designspaces without <instances> (5626514).
• Updated minimum installation requirements:
  • fonttools >= 3.21.1
  • cu2qu >= 1.3.0
  • glyphsLib >= 2.2.1
  • ufo2ft >= 1.1.0
  • MutatorMath >= 2.1.0
  • defcon >= 0.3.5
  • booleanOperations >= 0.8.0