Improve error handling, critical needs input

[riston]

There are some cases where the response is not handled correctly, this seems to be faulty on Desk side but also needs handling in library.

Also it would be good to expose the request timeout module option for longer requests like >3 seconds.

The error looks like this, the body is not containing the result object:

/app/node_modules/desk.js/lib/client.js:133
    if (response.statusCode > 299 && 'message' in body)
                                                  ^
TypeError: Cannot use 'in' operator to search for 'message' in undefined
    at Client.onResponse (/app/node_modules/desk.js/lib/client.js:133:51)
    at Request._callback (/app/node_modules/desk.js/node_modules/async/lib/async.js:597:23)
    at Request.self.callback (/app/node_modules/desk.js/node_modules/request/request.js:129:22)
    at emitTwo (events.js:87:13)
    at Request.emit (events.js:172:7)
    at Request.<anonymous> (/app/node_modules/desk.js/node_modules/request/request.js:873:14)
    at emitOne (events.js:82:20)
    at Request.emit (events.js:169:7)
    at IncomingMessage.<anonymous> (/app/node_modules/desk.js/node_modules/request/request.js:824:12)
    at emitNone (events.js:72:20)

Also made the PR for the error handling #15