Button wishlist

Button is currently tagged as a Beta component, and in order to remove that label, it needs to have a stable architecture and API. This living document will track some of the remaining items that need to be done to consider moving Button out of Beta.

To-do:

• Default Y.Button's BOUNDING_TEMPLATE to <button type="button"> (src)
• Make ButtonGroup widget single-box (src)
• Make cssbutton more skinnable (involves breaking up the CSS into multiple files)
• Introduce toggle plugin (src)
• Improve documentation & examples
• Add performance tests

Done:

• Preserve Y.Button node attributes on render()
• Added HTML support for Button labels