add forward mode

[mimmi20]

This PR tries to add a forward mode (you may have a better name).

If this mode is activated via config, an composer install and an composer update call is forwarded to all namespaced bin directories with all parameters. Setting up post-install-cmd or post-update-cmd in composer.json is not required to update namespaced bin directories.

This is related to #61, #65 and #66

[theofidry]

Thanks for the PR!

Looks good for me overall, I would just add a doc entry for it as well :)

[theofidry]

Thank you @mimmi20 !