Handle LinkedIn errors inside library to pass them as `err` to callback

[irnc]

Right now LinkedIn errors are not passed as err to callback.

By LinkedIn error I mean HTTP response with status code not equal to 200 and with response body with errorCode property.

For now only connection level errors are passed as err (this is behaviour inherited from request module).

Are you ok to receive pull request which implement passing LinkedIn errors to callback as err?

[ArkeologeN]

Yeah that's fine. Sound's good. Nice idea. Lets do it!

[ArkeologeN]

But we'll take care if we still throw Error object wrapped up over the status error etc thrown by LinkedIn?

So, it will make something like this:

// If something wrong happened with status & request code is != 200
throw Error('put_linkedIn_error_message_here');