Add onStop callback which is called when a device is stopped either explicitly or internally as a result of an error.

The rationale for this change is to keep it consistent with the rest of the library.

Rename mal_device__read_samples_from_client() to mal_device__read_frames_from_client() and mal_device__send_samples_to_client() to mal_device__send_frames_to_client().

Rationale for this is to keep it consistent with the rest of the library.

The rationale for this change is that during testing I noticed that
snd_pcm_open() would sometimes fail with "Invalid value for card"
when using the "NAME" hint returned by snd_device_name_get_hint()
verbatim. Using "hw:%d,%d" seems to fix this problem.

 - The buffer size is now set with set_buffer_size_near()
 - The size of the buffer is now independant of periods
 - snd_pcm_sw_params_set_avail_min() is now called with the previous
   power of 2 rather than the next.
 - The start threshold is now called with the previous power of 2
   rather than the next.

  - mal_device_get_available_rewind_amount()
  - mal_device_rewind()