Make ProcessCallbacks struct public

[Davvos11]

Changes:

Made ProcessCallbacks public in lib.rs.

Why?

When creating an AsyncClient using client.activate_async and using a handler with state, the ProcessCallbacks type is needed if you want to annotate the type of the AsyncClient

For example:

fnsome_function() -> anyhow::Result<AsyncClient<Notifications,ClosureProcessHandler<State,ProcessCallbacks<implFnMut(&mutState,&Client,&ProcessScope) -> Control,implFnMut(&mutState,&Client,Frames) -> Control>>>>{let process_callback = move |state:&mutState,client:&Client,ps:&ProcessScope| -> Control{Control::Continue};let buffer_callback = |state:&mutState,client:&Client,len:Frames| -> Control{Control::Continue};let handler = ClosureProcessHandler::with_state(Jack::default(), process_callback, buffer_callback);let active_client = client.activate_async(notifications, handler)?;Ok(active_client)}

[Davvos11]

I found that I can also type the client using impl ProcessHandler to avoid this issue:

fn some_function() -> anyhow::Result<AsyncClient<Notifications,implProcessHandler>{