refactor: Refactored the library file tree

Resolves #249

example/capacitor_time_curve.cpp

@@ -20,10 +20,10 @@
     physical_quantities
 */
 
-#include <units/physical/si/derived/capacitance.h>
-#include <units/physical/si/derived/resistance.h>
-#include <units/physical/si/base/time.h>
-#include <units/physical/si/derived/voltage.h>
+#include <units/physical/si/capacitance.h>
+#include <units/physical/si/resistance.h>
+#include <units/physical/si/time.h>
+#include <units/physical/si/voltage.h>
 #include <units/math.h>
 #include <units/quantity_io.h>
 #include <iostream>