Added "Add to party"

An user in itch.io reported to be confused about adding the character with the command later, which a need for extended use, having to manage the variables. I added an option to "add to party" once it is created.
Besides that, I also fixed a couple of errata that could easily lead into crash depending on use.
I also took the chance to remove redundancy, there were three commands for two options, so I made them one single argument in the basic command.