Handle loose ends in `module` core command implementation

[ZeroKnight]

There are a few TODOs revolving around the module core command implementation.

• [x] Need proper exceptions for module lookups/loading attempts. See #6.
  • Unable to differentiate:
  • Failure to reload
  • Attempt to reload a module that isn't loaded (or doesn't even exist)
• [x] Don't duplicate module lookup logic across subcommands
• [x] Handle multiple module arguments (load, reload, info)
  • Aggregate results in a single message