Libmpv2-rs version 4.1.0

Changes:

• Add mpv_render_context_update @ianhattendorf

Bug fixes:

• Fixed signed chars causing compilation issues on aarch64 @ianhattendorf

Libmpv2-rs version 4.0.0

Changes:

• Removed all command helpers. Use mpv.command directly instead.
• Removed MpvNode.value() and MpvNodeValue. Use MpvNode directly
• Moved libmpv2::MpvNode to libmpv2::mpv_node::MpvNode
• Changed MpvNode.to_f64(), .to_bool(), ... to MpvNode.f64(), .bool(), ...
• MpvNode.array() and MpvNode.map() now own self
• MpvNode now implements Eq

Bug fixes:

• Fixed opengl example
• Fixed use-after-free bug with MpvNode