Add a more thorough C test/example
Add a more thorough C test/example

Shows how to use the GSound API from C. It also tests the
cancellation of two playing sounds at once, and cancellation
from a different thread.

It all seems to work without any problems, at least on my system
with the pulse driver.

GNOME/gsound,GNOME/gsound,tcbrindle/gsound,tcbrindle/gsound