Allow specifing password as argument

[goodevilgenius]

When reading an encrypted PDF, stapler asks for a password to decrypt it. This makes it difficult to script this behavior.

It would be useful if the decryption passphrase could be specified as a command-line argument so that no user interaction is required.

[hellerbarde]

that is a good idea. I am in the process of rewriting the command parsing code. I will try to incorporate this.