v0.3.0

• Added box: a casing drawn behind the label that follows the curve at the
  label's height, under the glyphs, so the label stays legible where it crosses
  the lines it labels. Because it is a single fill it gives solid coverage
  behind plain and mathtext alike, unlike a wide path_effects stroke, which
  cannibalizes adjacent per-character glyphs. Accepts True, a color string, or
  a dict of color / pad / alpha.
• Mathtext runs now honor path_effects, matching the per-character glyphs, for
  a lighter glyph-hugging casing (a white withStroke). Path effects already
  reached plain characters through the keyword pass-through; mathtext runs draw
  their own path and previously skipped them.
• Fixed mathtext vertical alignment: a run now rides the curve on the
  surrounding text's x-height line rather than its own bounding box, so a
  superscript or tall delimiter no longer drops the body below the neighbouring
  plain characters.