0.2.0

Added

• PiRationalFormatter that prints rational multiples of pi.
• zero_props and pole_props argument to plane_plots.*plane*-functions
  that allows more detailed styling of pole/zero markers.
• multiplicity_props argument to plane_plots.*plane*-functions that allows
  styling of pole/zero multiplicity texts.
• This changelog.

Fixed

• freq_unit was not propagated properly in all freq_plots.zfreq* functions and
  style-combinations.

Changed

• Change to src-layout