refactor: subcommand handling

[OfficialSirH]

WIP draft

• [x] implement interfaces that will make subcommand implementations simple and w/o redundancy
• [x] create a subcommand directory that will contain a folder named after each command that has subcommand(s)
• [x] implement a way for the command handler to run down all of the available subcommands and merge them with their parent command

[OfficialSirH]

Currently got subcommand implementation, registering with parent command, and handling completed. The main thing left over is to make sure it's functional and clean before it's implemented for all of the commands that have subcommands.

[OfficialSirH]

Have you tested your changes?

I have not. I'll try to do that soon.

[OfficialSirH]

@didinele Tested it and the subcommand handling works perfectly.