* wayland: don't create a second event_queue
As each EventsLoop has its own context, this is no longer necessary.
* wayland: buffer events rather than direct dispatch
Changes the behavior of the event loop to first internally
buffer the events generated by the wayland handlers, and then
dispatch them to the client's closure.
- It simplifies the event loop logic
- It makes it possible for the user to call window methods such as
`set_title()` or `set_inner_size()` without causing a deadlock
* wayland: add is_ready() & fix protocol errors
Adds a `is_ready()` method to the windows to advertize
when it is legal to start drawing, and fix a few wayland
protocol mishandling in the process.