Fix Go build due to enum casting (#164)

* fix go build due to enum casts by casting enum array explicitly

rtaudio_c.cpp

@@ -17,9 +17,10 @@ struct rtaudio {
 
 const char *rtaudio_version() { return RTAUDIO_VERSION; }
 
-extern "C" const rtaudio_api_t rtaudio_compiled_apis[]; // casting from RtAudio::Api[]
-extern "C" const unsigned int rtaudio_num_compiled_apis;
-const rtaudio_api_t *rtaudio_compiled_api() { return rtaudio_compiled_apis; }
+extern "C" const RtAudio::Api rtaudio_compiled_apis[];
+const rtaudio_api_t *rtaudio_compiled_api() {
+  return (rtaudio_api_t *) &rtaudio_compiled_apis[0];
+}
 
 extern "C" const char* rtaudio_api_names[][2];
 const char *rtaudio_api_name(rtaudio_api_t api) {