add extern "C" wrapping to rbs.h when using C++

Author: froydnj

include/rbs.h

@@ -1,6 +1,14 @@
 #ifndef RBS_H
 #define RBS_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include "rbs/parser.h"
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif