Removed macro for explicitly requiring experimental optional and updated README to reflect the change

Author: cbeiraod

README.md

@@ -325,7 +325,7 @@ int main() {
 
 If you do not have C++17 support, you can use boost optional instead by defining `_MODERN_SQLITE_BOOST_OPTIONAL_SUPPORT` before importing the `sqlite_modern_cpp` header.
 
-If your compiler does support C++17, but does not have optional (macOS for instance, at the time this was written), you can use std::experimental::optional instead by defining `_MODERN_SQLITE_EXPERIMENTAL_OPTIONAL_SUPPORT` before importing the `sqlite_modern_cpp` header.
+If the optional library is not available, the experimental/optional one will be used instead.
 
 **Note: boost support is deprecated and will be removed in future versions.**
 

hdr/sqlite_modern_cpp.h

@@ -17,11 +17,9 @@
 #if __cplusplus > 201402 && __has_include(<optional>)
 #define MODERN_SQLITE_STD_OPTIONAL_SUPPORT
 #elif __has_include(<experimental/optional>)
-#ifdef _MODERN_SQLITE_EXPERIMENTAL_OPTIONAL_SUPPORT
 #define MODERN_SQLITE_EXPERIMENTAL_OPTIONAL_SUPPORT
 #endif
 #endif
-#endif
 
 #ifdef __has_include
 #if __cplusplus > 201402 && __has_include(<variant>)