Update to latest RtAudio (as submodule). Support for runtime selection of audio driver.

Here we migrate the "burned-in" RtAudio support to utilize the official github version.

Costs:

• use of submodules may be a headache across branches. Or for non-pro-level git users.

Benefits:

• latest and greatest RtAudio
• ability to have multiple drivers in the same chuck build. Currently we have validated cohabitation of Windows ASIO and DirectSound as well as Pulse, Alsa and Jack drivers in the same linux build.

Known issues:

• RtAudio no longer throws exceptions and some of the error reporting codepaths haven't been fully tested.

Usage/testing:

• no changes to the default builds have been made. And should still produce the same result. If one edits a makefile or vsproj to include more RtApi driver requests (eg -D__WINDOWS_ASIO__) you can include multiple drivers in your build. A new commandline option --driver is required to select the non-default driver... For example: chuck --probe --driver::ASIO vs chuck --probe

These build failures are due to the fact that the automation build hasn't properly initialized the new RtAudio submodule.