Load and dump subcommands shouldn't accept arbitrary keyword arguments

Because of a quirk of fire, the load and dump subcommands can't be used with flags (like `--help`) after them because they take `**kwargs`.

Start by locating the command-line entry point and the load and dump subcommands, then reproduce the issue with flags such as --help placed after each subcommand. Trace how Fire interprets their **kwargs parameters. Done means load and dump no longer accept arbitrary keyword arguments and flags after them work as expected.

Written by the indexing model from the issue text.