options constructor accepts a context object

[DonutEspresso]

I'm finding I frequently want to add contextual properties to an object I'm creating to store some context about what might have caused that error. i.e., if an http request failed, I might want to put the url on the error object.

Since we already have the options constructor, this seemed like a good place to put it. All arbitrary context properties are stored on the context property instead of directly on the error itself.

Suggestions/feedback @yunong @micahr?

[DonutEspresso]

BTW, the intent is to use this in conjunction with bunyan. Sometimes I want to propagate an error up two or three callbacks before logging it out - but I've lost the context by then. This allows me to keep that context tied with the error.

The context property is ignored when calling toJSON() or toString() in the event it is sent out over the wire.

[micahr]

Looks good to me, @DonutEspresso

[DonutEspresso]

Looks like we're all on board - may have to come up with some custom serializers for bunyan to support dumping of context.