Request proxy support

[Asp3ctus]

Added a request proxy support

I think it is needed feature for this king of module :)

[stevebest]

There must be a better way to pass goodiness to request without turning API into a swiss army knife with a kitchen sink. And I'm kinda working on it.

Thanks for calling it a 'king of module', anyways. :)

[Asp3ctus]

LOL ... miss spelled king - kind :) If you add this feature in different way it be better ...

[AlexeyKupershtokh]

You should probably add an ability for dependency injection for request using request.defaults({}) then:

var vk = vkontakte('CLIENT ID', 'CLIENT SECRET');
vk.setRequest(request.defaults({proxy: ...}));
vk('users.get', { uid: 1, fields: 'uid,first_name,photo' }, function (err, user) {
  console.log(user);
});

Unfortunately since you don't use oop, it's harder to implement.