day-night loop, dynamic skybox, clock on debug panel

src/util/timeutil.h

@@ -0,0 +1,9 @@
+#ifndef UTIL_TIMEUTIL_H_
+#define UTIL_TIMEUTIL_H_
+
+namespace timeutil {
+    float time_value(float hour, float minute, float second);
+    void from_value(float value, int& hour, int& minute, int& second);
+}
+
+#endif // UTIL_TIMEUTIL_H_