Fix #485: Reject invalid args and allow positional args

[spinualexandru]

• Added rejections for invalid arguments
• Added positional arguments so in case you are running "edit -- -?" it will allow you to create a file called "-?"

Closes #485

[lhecker]

While I think that your PR generally went into the right direction, I've reduced its complexity a bit to address the issue first, by removing the logic to reject invalid arguments.