optparse-applicative 0.18.0

• Move to 'prettyprinter` library for pretty printing.

  This is a potentially breaking change when one uses the '*Doc' family of functions
  (like headerDoc) from Options.Applicative. However, as versions of
  'ansi-wl-pprint > 1.0' export a compatible Doc type, this can be mitigated by
  using a recent version.

  One can also either import directly from Options.Applicative.Help or from the
  Prettyprinter module of 'prettyprinter'.

• Allow commands to be disambiguated in a similar manner to flags when the
  disambiguate modifier is used.

  This is a potentially breaking change as the internal CmdReader constructor
  has been adapted so it is able to be inspected to a greater degree to support
  finding prefix matches.