Libmpv-rs version 2.0.0

This release fixes UB around events that unfortunately got introduced during a recent refactor.
The recently added MpvNodes can now be observed as properties.

Changes:

• Add method Mpv::with_initializer to set options before initialization
• [breaking] Borrow &mut self in wait_event to disallow using two events where the first points to data freed in the second wait_event call
• [breaking] PropertyData<'_> is no longer Clone or PartialEq, Event<'_> is no longer Clone to avoid cloning/comparing MpvNode

Contributors:
@yaymukund (MpvNode changes)