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- snakeoil.cli.arghparse: Drop default subparser support.
- snakeoil.cli.arghparse: Run multiple registered final check functions,
previously only the last registered function would be run.
- snakeoil.cli.arghparse: Add positive_int and bounded_int argparse types.
- snakeoil.cli.arghparse: Add bind_pre_parse() to support running a decorated
function for pre-parsing parser manipulation purposes.
- Add py3.8 support.