refactor: Refactored the library file tree

Resolves #249

test/unit_test/static/fps_test.cpp

@@ -21,16 +21,16 @@
 // SOFTWARE.
 
 #include <units/physical/si/fps/fps.h>
-#include <units/physical/si/derived/acceleration.h>
-#include <units/physical/si/derived/area.h>
-#include <units/physical/si/derived/energy.h>
-#include <units/physical/si/derived/force.h>
-#include <units/physical/si/base/length.h>
-#include <units/physical/si/base/mass.h>
-#include <units/physical/si/derived/power.h>
-#include <units/physical/si/derived/pressure.h>
-#include <units/physical/si/derived/speed.h>
-#include <units/physical/si/base/time.h>
+#include <units/physical/si/acceleration.h>
+#include <units/physical/si/area.h>
+#include <units/physical/si/energy.h>
+#include <units/physical/si/force.h>
+#include <units/physical/si/length.h>
+#include <units/physical/si/mass.h>
+#include <units/physical/si/power.h>
+#include <units/physical/si/pressure.h>
+#include <units/physical/si/speed.h>
+#include <units/physical/si/time.h>
 
 namespace {