Added wrapper option

[kajetan-nobel]

Needed option in #26

Example of use:

var rellax = new Rellax('.rellax', {
    wrapper: document.querySelector('.wrapper') // DOMElement
});

or

var rellax = new Rellax('.rellax', {
    wrapper: '.wrapper' // selector
});

[kajetan-nobel]

I added also refresh method to handle by own window resize or reload elements

[bpongy]

not necessary with center: true option.
#36

[kajetan-nobel]

@redpik without that scroll event is not handled. In my example you scroll wrapper, not document (document is with overflow hidden).

[tonyyb]

👍 for refresh function !
When will it be published ?

[nizulzaim]

@routegroup , i am sorry. i want to know if using this wrapper option, it detect the wrapper offsetX and offsetY rather than window offset? if the answer yes, from my understanding it is possible to use it with custom scrollbar #65. @tonyyb, i think someone need to maintain this project. I also think this project already abandon by the owner

[mralessio]

Need it too. Any plans to merge it?

[jvrdom]

This will be awesome to use, need it too.

[kajetan-nobel]

I merge master to this PR. If you need any changes about this PR please tell me.