Effects will now be implemented by plugging effect nodes into the node
graph at the appropriate location.

With this change, attachment and detachment of a node's output bus is
now consistent:

  * ma_node_attach_output_bus()
  * ma_node_detach_output_bus()

The old function that allowed you to attach the other way around has
been removed as the caller can easily do that themselves by swapping
the order of parameters.

This changes the way ma_node_uninit() waits for the audio thread. Now,
instead of waiting for the *entire* graph to complete, it only waits
for it's local processing to complete.

This makes it possible to give individual input and output buses unique
channel counts which might be useful for specific kinds of effects.

This also silences a warning on GCC.

Remove some warnings (warning C4100: unreferenced formal parameter)

Fix issue #252

Public issue https://github.com/mackron/miniaudio/issues/251

Public issue https://github.com/mackron/miniaudio/issues/101

Public issue https://github.com/mackron/miniaudio/issues/237

Public issue https://github.com/mackron/miniaudio/issues/237