Addresses issue #17.

What a nightmare!

MAL_CHANNEL_MONO was previously an alias of MAL_CHANNEL_FRONT_CENTER.

This reason for this change is that it does not suit the trial and
error architecture of mini_al's backend initialization.

mal_context.pulse.tryAutoSpawn can be used to enable auto-starting.

This commit also fixes a bad bug where initialization will always fail
when initializing from memory.

The reason for this change is to ensure OSS is chosen over JACK by
default on BSD platforms.

APIs are now per-context rather then per-device. This is leftover from
the no-context-API days.