Proposal: orders.on_next_render

[MartinKavik]

See #204 (comment).

This function would be probably used as the alternative for requestAnimationFrame, did_mount and combination should_render_now + send_msg.

We should test it with some examples (especially with animation_frame) before we decide how should the final API look like.

The first suggestion:

orders.on_next_render(|timestamp| { 
    ...
    Msg::NoOp
})

[MartinKavik]

@MartinKavik Refactor referenced PR.