Breaking Changes
- `*DataExt` traits removed; now `*Data` types wrap custom data.
  * Any calls to `Proxy::data` will need to be updated for new type.
- All `delegate_*!` macros except `delegate_registry!` replaced with single
  `delegate_dispatch2!` in preparation for future wayland-rs release.

Fixed
- Prevent popup reposition request if `xdg_popup` version is below 3.

Additions
- Add support for `xdg_wm_dialog` v1.
- Add support for `xx_input_method` v1.
- Add support for `xx_keyboard_filter` v1.
- Add support for `ext-background-effect` v1.