Update to 0.1.5.2

changes from README:
 - The 0.1.5.2 release fixes some missing documentation.
 - The 0.1.5.1 release fixes some warnings and stuff.
 - The 0.1.5 release includes the "soft dash" option, giving the ability to
   allow positional arguments to begin with a dash if possible.
 - The 0.1.4 release includes the ability to mix optional and required
   positional arguments.
 - The various 0.1.3.x point releases include bug fixes and various
   extra-minor enhancements. See the Git log.
 - The 0.1.3 release includes more uniform and usable error handling.