Add adl_ranges (#413)

Co-authored-by: lsemprini <17140216+lsemprini@users.noreply.github.com>

doc/limitations.md

@@ -23,6 +23,32 @@
 
 * If an enum is declared as a flag enum, its zero value will not be reflected.
 
+* Or, for enum types that are deeply nested in classes and/or namespaces, declare a function called `my_adl_info_struct adl_magic_enum_define_range(my_enum_type)` in the same namespace as `my_enum_type`, which magic_enum will find by ADL (because the function is in the same class/namespace as `my_enum_type`), and whose return type is a struct with `static constexpr` data members containing the same parameters as `magic_enum::customize::enum_range<my_enum_type>`
+  ```cpp
+  namespace Deeply::Nested::Namespace {
+  enum class my_enum_type { ... };
+  struct my_adl_info_struct {
+    static constexpr bool is_flags = true;
+    // you can also set min and max here (see Enum Range below)
+    // static constexpr int min = ...;
+    // static constexpr int max = ...;
+  };
+  // - magic_enum will find this function by ADL
+  // - no need to ever define this function
+  my_adl_info_struct adl_magic_enum_define_range(my_enum_type); 
+  }
+  ```
+
+* As a shorthand, if you only want to set `is_flags` and not `min` or `max`, you can also use `magic_enum::customize::adl_info<is_flags_bool>` to avoid having to define `my_adl_info_struct` in your code:
+  ```cpp
+  namespace Deeply::Nested::Namespace {
+  enum class my_enum_type { ... };
+  // - magic_enum will find this function by ADL
+  // - no need to ever define this function
+  magic_enum::customize::adl_info<true> adl_magic_enum_define_range(my_enum_type); 
+  }
+  ```
+
 ## Enum Range
 
 * Enum values must be in the range `[MAGIC_ENUM_RANGE_MIN, MAGIC_ENUM_RANGE_MAX]`.
@@ -52,6 +78,32 @@
   };
   ```
 
+* Or, for enum types that are deeply nested in classes and/or namespaces, declare a function called `my_adl_info_struct adl_magic_enum_define_range(my_enum_type)` in the same namespace as `my_enum_type`, which magic_enum will find by ADL (because the function is in the same class/namespace as `my_enum_type`), and whose return type is a struct with `static constexpr` data members containing the same parameters as `magic_enum::customize::enum_range<my_enum_type>`
+  ```cpp
+  namespace Deeply::Nested::Namespace {
+  enum class my_enum_type { ... };
+  struct my_adl_info_struct {
+    static constexpr int min = 100;
+    static constexpr int max = 300;
+    // you can also set is_flags here
+    // static constexpr bool is_flags = true;
+  };
+  // - magic_enum will find this function by ADL
+  // - no need to ever define this function
+  my_adl_info_struct adl_magic_enum_define_range(my_enum_type); 
+  }
+  ```
+
+* As a shorthand, if you only want to set `min` and `max` and not `is_flags`, you can also use `magic_enum::customize::adl_info<min_int, max_int>` to avoid having to define `my_adl_info_struct` in your code:
+  ```cpp
+  namespace Deeply::Nested::Namespace {
+  enum class my_enum_type { ... };
+  // - magic_enum will find this function by ADL
+  // - no need to ever define this function
+  magic_enum::customize::adl_info<100 /*min*/, 300 /*max*/> adl_magic_enum_define_range(my_enum_type); 
+  }
+  ```
+
 ## Aliasing
 
 magic_enum [won't work if a value is aliased](https://github.com/Neargye/magic_enum/issues/68). How magic_enum works with aliases is compiler-implementation-defined.