(https://github.com/ruby/irb/pull/886)
This is a feature that has been requested for a long time. It is now
possible to define custom commands in IRB.
Example usage:
```ruby
require "irb/command"
class HelloCommand < IRB::Command::Base
description "Prints hello world"
category "My commands"
help_message "It doesn't do more than printing hello world."
def execute
puts "Hello world"
end
end
IRB::Command.register(:hello, HelloCommand)
```
888643467c
