dom/document: remove double #inspect implementation
browser: update to master opal
browser: require native stdlib
dom/node_set: use Native.convert instead of Native.try_convert
socket: fix creation on WebKit
window: add #close
Merge pull request #3 from opal/window-close

window: add #close
window: add #prompt and #confirm dialogs
dom/element: fix scroll.to implementation

scrollTo isn't defined for Element, got the same result by combining 
scrollTop and scrollLeft.

ref: https://developer.mozilla.org/en-US/docs/Web/API/Element
dom/element: add scroll.width and scroll.height

refs: 
https://developer.mozilla.org/en-US/docs/Web/API/Element.scrollHeight
https://developer.mozilla.org/en-US/docs/Web/API/Element.scrollWidth
socket: typo
spec: move to rspec