Rename alcGetLatency to ALCdevice_GetLatency
Make LockContext and UnlockContext inline again
Set vtables in the constructor
Convert the OSS backend to the new interface
Make backend factory methods static as needed
Constify some function pointers
Rename VCALL and VCALL0 to V and V0
Use a unique backend type for loopback
Only set device functions when needed
Use C99 inline semantics