entry_point for command line tools
entry_point for command line tools

The command line tool now uses setuptools' `entry_point` argument to
construct command line scripts, rather than the explicit scripts of the
`bin` directory.

We retain the scripts for now, since they are probably used in testing,
but may phase them out at some point if it's safe.

marshallward/payu,marshallward/payu,nicjhan/payu,aidanheerdegen/payu,aidanheerdegen/payu