Some refactoring to the PulseAudio backend.

The PulseAudio mainloop and context objects have been moved out of the
device and into the context.

tests/test_deviceio/ma_test_deviceio.c

@@ -579,5 +579,10 @@ done:
         ma_encoder_uninit(&g_State.encoder);
     }
 
+
+    printf("Press Enter to quit...");
+    getchar();
+    getchar();
+
     return 0;
 }