autoregister cqrs handlers fails to handle sub dirs

Bug Report

Summary

e.g. in users there are braintree commands within the commands dir. After auto registering the commands dir:

     NexusCqrs::CommandBus::UnregisteredHandler:
       Missing handler for Commands::Braintree::RequestSubscriptionCancellation

Steps to reproduce

Run tests in web-dev/users#458

What is the expected behaviour?

All command handlers should be registered below the supplied dir, recursively.

Other information

Attempting to register the subdir encounters another error involving dupe classes.

NexusCqrs::CommandBus::MultipleHandlers:
  Multiple handlers not allowed for Commands::CreateRole
# /usr/local/bundle/gems/nexus_cqrs-0.4.0/lib/nexus_cqrs/command_bus.rb:28:in `register'

Expected since autoregister proceeds to check the entire ObjectSpace, does not appear to be designed to be run twice with the same base_class.

Expect we can resolve by changing the ruby directory pre processing to iterate recursively.

Perhaps (not tried):

      Dir["#{dir}/**/*.rb"].each do |file|

Checklist

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