Add support for per-device master volume control.

New Device APIs:
  * ma_device_set_master_volume()
  * ma_device_get_master_volume()
  * ma_device_set_master_gain_db()
  * ma_device_get_master_gain_db()

New Helper APIs
  * ma_copy_and_apply_volume_factor_u8()
  * ma_copy_and_apply_volume_factor_s16()
  * ma_copy_and_apply_volume_factor_s24()
  * ma_copy_and_apply_volume_factor_s32()
  * ma_copy_and_apply_volume_factor_f32()
  * ma_apply_volume_factor_u8()
  * ma_apply_volume_factor_s16()
  * ma_apply_volume_factor_s24()
  * ma_apply_volume_factor_s32()
  * ma_apply_volume_factor_f32()
  * ma_copy_and_apply_volume_factor_pcm_frames_u8()
  * ma_copy_and_apply_volume_factor_pcm_frames_s16()
  * ma_copy_and_apply_volume_factor_pcm_frames_s24()
  * ma_copy_and_apply_volume_factor_pcm_frames_s32()
  * ma_copy_and_apply_volume_factor_pcm_frames_f32()
  * ma_copy_and_apply_volume_factor_pcm_frames()
  * ma_apply_volume_factor_pcm_frames_u8()
  * ma_apply_volume_factor_pcm_frames_s16()
  * ma_apply_volume_factor_pcm_frames_s24()
  * ma_apply_volume_factor_pcm_frames_s32()
  * ma_apply_volume_factor_pcm_frames_f32()
  * ma_apply_volume_factor_pcm_frames()
  * ma_factor_to_gain_db()
  * ma_gain_db_to_factor()