Kubectl / git like plugin system

[luisdavim]

It would be nice to be able to specify a prefix and if a subcommand is not found look for an executable in the PATH that matches prefix-subcommand and execute it if found, passing any args and flags to that executable. Like git and kubectl do.

[luisdavim]

Another option could be to allow defining a catchall handler if no subcommand matches, that would make implementing the above simple.