... in addition to spectrograms.

- The option argument to `collectExample()` now has a new field called
  "includeTimeDomainWaveform". If set to true, the collected example
  will include the raw audio waveform. Obviously, use caution when using
  this feature as it'll increase the memory consumption of the examples
  by a few times.
- The demo page now has a new checkbox called "Include audio waveform"
  that demonstrates this new feature, along with the playback of the audio
  waveforms through WebAudio.
- Add `speechCommands.utils.playRawAudio()`.