using atomics is no longer the default: ENTT_NO_ATOMIC -> ENTT_USE_ATOMIC

TODO

@@ -27,7 +27,6 @@
 * meta: members+class as fake functions, is it possible?
 * meta: are fake types not backed by actual types possible?
 * meta: export implicitly generated named types if possible
-* flip ENTT_NO_ATOMIC and make it opt-in rather than opt-out
 * welcome -ftime-trace to inspect compilation time
 * add meta support to registry:
   - entity for each component

src/entt/config/config.h

@@ -17,12 +17,12 @@
 #endif // ENTT_HWS_SUFFIX
 
 
-#ifndef ENTT_NO_ATOMIC
+#ifndef ENTT_USE_ATOMIC
+#define ENTT_MAYBE_ATOMIC(Type) Type
+#else // ENTT_USE_ATOMIC
 #include <atomic>
 #define ENTT_MAYBE_ATOMIC(Type) std::atomic<Type>
-#else // ENTT_NO_ATOMIC
-#define ENTT_MAYBE_ATOMIC(Type) Type
-#endif // ENTT_NO_ATOMIC
+#endif // ENTT_USE_ATOMIC
 
 
 #ifndef ENTT_DISABLE_ETO