* Major library cleanup and API simplification.  Eliminates old,
  dead, or redundant code that had accrued over time.  Exposes patp,
  patp2dec, patp2hex, and hex2patp functions as the API core (and
  similarly for @q).

* Adds proper in-library documentation, and beefs up the README.

* Adds property tests for both internals and exposed functions.

* Standardises output, e.g. by always including a leading tilde in
  @p values.