debug module with dynamic behavior (enable/disable in runtime)

[ibc]

Hi, I've sent a PR to the debug module project adding the capability of dynamic debug instances that can be enabled/disabled in runtime (this is, without having to restart the application):

• Add optional dynamic debug instances (react on enable() and disable() once created) debug-js/debug#209

I expect this to be also useful for express applications, so I wonder if you could provide some feedback on the PR :)

[dougwilson]

I am pretty indifferent, as we'll use whatever the default we get (i.e. we'll only ever use the require('debug')('<name') method unless we can't any more. If this requires us to pass in a new option, then we'd pass, because the only way we could promote this well would be a massive updating of all our dependents.