Represents a server response.
@class Response
@constructor
@param {Function} cb Callback to be used when the response is
finished. See the `end` event on the `on` method documentation.
 
Response body.

@attribute body
@type Buffer
 
Response status code (by default, `200`).

@attribute statusCode
@type Integer
 
Response headers. Note that the header names are Node-style
(ie. lowercase).

@attribute headers
@type Object
 
Whether the response is finished.

@attribute ended
@type Boolean
function Response(cb) {
        this.body       = new Buffer(0);
        this.statusCode = 200;
        this.headers    = {};
        this.ended      = false;
        var endHandlers = [];
        if (typeof cb === 'function') { endHandlers.push(cb); }
        this._eventHandlers = {head: [], data: [], end: endHandlers};
    }