Changed stdout documentation to detail the 's' paramater

[tomkadwill]

Changed stdout documentation to reference the s parameter. stdout will no longer be flagged by rdoc as having an undocumented parameter.

This is my first Ruby documentation commit so let me know if I need to change anything :)

[vipulnsward]

stdout is more readable. wdyt about changing this to

# Sets the IO used as +stdout+. Defaults to STDOUT
      def stdout=(stdout)
        @stdout = stdout
      end

[tomkadwill]

@vipulnsward Yes I think that does look better. I was thinking about that but didn't know whether it was called s for a reason. I've updated my PR to reflect the change that you suggested.

[tomkadwill]

Any update on this? I would like to carry on documenting debug.rb but not sure if this change is good :)

/cc @zzak @nobu