refactor: add C++17 compatibility

Author: Wend4r

include/plugify/any.hpp

@@ -1,9 +1,9 @@
 #pragma once
 
-#include <plugify/numerics.hpp>
-#include <plugify/string.hpp>
-#include <plugify/variant.hpp>
-#include <plugify/vector.hpp>
+#include "numerics.hpp"
+#include "string.hpp"
+#include "variant.hpp"
+#include "vector.hpp"
 
 namespace plg {
 	struct invalid {}; //!< Represents an invalid type.

include/plugify/macro.hpp

@@ -125,3 +125,26 @@
 #else
 #  define PLUGIFY_RESTRICT
 #endif
+
+#if __cplusplus >= 202002L
+// Include it in your implimentation
+// #  include <concepts>
+// #  include <memory>
+
+#  define PLUGIFY_INPUT_ITERATOR std::input_iterator
+#  define PLUGIFY_CONSTRUCT_AT(ptr, ...) std::construct_at(ptr, __VA_ARGS__)
+#else // !(__cplusplus >= 202002L)
+#  define PLUGIFY_INPUT_ITERATOR typename
+#  define PLUGIFY_CONSTRUCT_AT(ptr, ...) new (ptr) std::remove_reference_t<decltype(*ptr)>(__VA_ARGS__)
+#endif // __cplusplus >= 202002L
+
+#ifndef __cpp_char8_t
+enum char8_t : unsigned char {};
+#endif // __cpp_char8_t
+
+#ifdef __cpp_lib_is_nothrow_convertible
+#  define PLUGIFY_NOTTHROW_CONVERTIBLE(T, S) std::is_nothrow_convertible_v<T, S>
+#else // !__cpp_lib_is_nothrow_convertible
+#  define PLUGIFY_NOTTHROW_CONVERTIBLE(T, S) 0
+#endif // __cpp_lib_is_nothrow_convertible
+