bypass ASIO SDK limitation of 1 device open at a time.

[rossb]

We currently use the C interface layer of the ASIO SDK (defined in asio.cpp) which only allows one driver to be loaded at a time. This is an artificial limitation which can be avoided by talking to the driver directly instead of calling the functions in asio.cpp.

The end goal would be to remove the following global reference from the code: extern AsioDrivers?* asioDrivers; And the implicit use of the global SDK variable theAsioDriver;

More research is required to determine exactly what needs to be done. Ideally we would like to avoid re-writing the whole ASIO sdk.