Added an option to create resizable windows on desktop.

You can also add callbacks that inform the application that the window was resized using GLView::addResizeCalback.
A dummy parameter was added to createWithRect in mobile mobile versions to keep them in sync.
Tested on Windows and iOS.
This is my first official contribution to this project - hope I did not break to many guidelines ;)
Yes this parameter is used only in the desktop version as there are no resizable windows on mobile devices. It is there just to keep everything compatible. because it is not really used in the mobile versions I used an odd name like _ignored_resizable instead of ignoredResizable - but I can change that if you think it would be better.