Compromise for changes in CMake build introduced by previous commit
that would interfere with use with add_subdirectory.

Re-adds:

- RTAUDIO_BUILD_TESTING
- RTAUDIO_BUILD_SHARED_LIBS
- RTAUDIO_BUILD_STATIC_LIBS

These now override BUILD_TESTING, BUILD_SHARED_LIBS, BUILD_STATIC_LIBS,
but only if they are defined and are not "".

- make build type a drop-down if it's not otherwise set.
- default to 'd' suffix for Windows debug builds only.

Analog of pr #190 for RtMidi.

Alsa API: Fix use of invalid card handle

WASAPI : Fixed #180 and reduced latency

Go with --with-dsound.

Fixes #144.

Fixes #142.