Refactor some cmd.js logic out into its own file for easier tests

While working on issue #69 I started to come across places where it was a little difficult to test if just a particular flag was called. I think it might help if some of the logic that is in cmd.js is broken out into its own file, so it would be easier to test if a particular flag was specified, and not necessarily test what that flag actually does. That could be done in its own separate test, where it would be easier to mock certain functions.

@richardlau @Trott thoughts?

I can send a PR so we can talk about it also

Commencez par lire cmd.js et identifiez la logique qui détermine si certains flags ont été spécifiés. Séparez cette logique dans son propre fichier afin de pouvoir la tester indépendamment, avec des fonctions simulées lorsque nécessaire. La tâche est terminée lorsque la détection des flags dispose de tests ciblés qui ne testent pas également ce que fait chaque flag.