The API now requires a command argument from signature. Parsing errors
(no command from input) is thrown as a custom exception, and caught by
the outmost possible invocation to emit a message from click.
I chose to make Script.parse to always operate in POSIX mode so it is much
easier to write commands compatible on all platforms.
Script.cmdify is the important part on Windows. It ensures the argument
line is always escaped and joined properly on Windows, not just for the
subset that works both under POSIX and Windows (as is the case of
shlex.escape).
Tzu-ping Chung