Pasts 0.12.0; `Microphone`, `Speakers` as `Notifier`

[AldaronLau]

• [x] Turn speakers and microphone into notifiers
• [x] Box microphone and speaker ffi as MicrophoneInner and SpeakerInner (soundness)
• [x] Update WebAssembly port
• [x] Doc tests
• [x] Query (default to 0 channels?)
• [x] Add changelog entry
• [x] Test WebAssembly port

[AldaronLau]

Closes https://github.com/libcala/wavy/pull/43