[ox/std] Add units.hpp to std.hpp and CMake install

(synced from 6ace1e641c)

src/ox/std/CMakeLists.txt

@@ -48,6 +48,7 @@ install(
 		trace.hpp
 		types.hpp
 		typetraits.hpp
+		units.hpp
 		vector.hpp
 	DESTINATION
 		include/ox/std

src/ox/std/std.hpp

@@ -25,4 +25,5 @@
 #include "typeinfo.hpp"
 #include "types.hpp"
 #include "typetraits.hpp"
+#include "units.hpp"
 #include "vector.hpp"