lib_commons: add a a lib_debug_print macro

Decision to keep a separate library debug level and macro and application debug level and application\nwas made to keep the library completely independent of any application.

lib_commons.h

@@ -11,6 +11,17 @@
 #define HARDWARE_VERSION_Z "hardware_version"
 #define HARDWARE_VERSION_H ""
 #define HARDWARE_VERSION "hardware_version"
+
+/*! @brief A macro for printing debug messages only if \<debug\> is true. */
+#define lib_debug_print(...)					\
+	do {									\
+		if (lib_debug)						\
+			fprintf(stderr, __VA_ARGS__);	\
+	} while (0)
+
+/*! @brief Variable used by debug_print, defined and initiated in dongle.c */
+extern int lib_debug;
+
 /**
  * Struct used for parsing the curl response from the dongle.
  */