This is the same as the normal ring buffer except everything is done in
terms of PCM frames instead of bytes. This is useful to simplify the
case of using the ring buffer for storing PCM audio data.

This is now stored separately for playback can capture in the playback
and capture sub-objects respectively.

This commit also renames the onLog member of mal_context_config to
logCallback for consistency with mal_device_config callback naming
convention.

There is now only a single API for initializing a device config which
is mal_device_config_init() and takes the device type as it's only
parameter. By default this will use the device's native configuration.

The device ID is also set in the device config. The next commits will
be changing mal_device_init() to remove the device type and ID from the
parameter list since they are now specified in the config.