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.
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