Simplify some C++ abstractions (#1518)

* Remove namespaces
* Prefer `bool operator==`, not `friend auto operator==`
* Prefer not to use `using`
* Use a `constexpr` function instead of a template for `flipTable`

src/gfx/reverse.cpp

@@ -12,7 +12,7 @@
 #include <string.h>
 #include <vector>
 
-#include "defaultinitalloc.hpp"
+#include "defaultinitvec.hpp"
 #include "file.hpp"
 #include "helpers.hpp" // assume