Reorganize directories (#3462)

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docs/mkdocs/docs/api/macros/nlohmann_json_serialize_enum.md

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+# NLOHMANN_JSON_SERIALIZE_ENUM
+
+```cpp
+#define NLOHMANN_JSON_SERIALIZE_ENUM(type, conversion...)
+```
+
+By default, enum values are serialized to JSON as integers. In some cases this could result in undesired behavior. If an
+enum is modified or re-ordered after data has been serialized to JSON, the later de-serialized JSON data may be
+undefined or a different enum value than was originally intended.
+
+The `NLOHMANN_JSON_SERIALIZE_ENUM` allows to define a user-defined serialization for every enumerator.
+
+## Parameters
+
+`type` (in)
+:   name of the enum to serialize/deserialize
+
+`conversion` (in)
+:   a pair of an enumerator and a JSON serialization; arbitrary pairs can can be given as comma-separated list
+
+## Default definition
+
+The macros add two friend functions to the class which take care of the serialization and deserialization:
+
+```cpp
+template<typename BasicJsonType>
+inline void to_json(BasicJsonType& j, const type& e);
+template<typename BasicJsonType>
+inline void from_json(const BasicJsonType& j, type& e);
+```
+
+## Notes
+
+!!! info "Prerequisites"
+
+    The macro must be used inside the namespace of the enum.
+
+!!! important "Important notes"
+
+    - When using [`get<ENUM_TYPE>()`](../basic_json/get.md), undefined JSON values will default to the first specified
+      conversion. Select this default pair carefully. See example 1 below.
+    - If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
+      list will be returned when converting to or from JSON. See example 2 below.
+
+## Examples
+
+??? example "Example 1: Basic usage"
+
+    The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM` can be used to serialize/deserialize both classical enums and
+    C++11 enum classes:
+
+    ```cpp hl_lines="16 17 18 19 20 21 22 29 30 31 32 33"
+    --8<-- "examples/nlohmann_json_serialize_enum.cpp"
+    ```
+
+    Output:
+    
+    ```json
+    --8<-- "examples/nlohmann_json_serialize_enum.output"
+    ```
+
+??? example "Example 2: Multiple conversions for one enumerator"
+
+    The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always
+    be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an
+    alternative *deserialization* from `"rot"` to `Color::red`.
+
+    ```cpp hl_lines="17"
+    --8<-- "examples/nlohmann_json_serialize_enum_2.cpp"
+    ```
+
+    Output:
+    
+    ```json
+    --8<-- "examples/nlohmann_json_serialize_enum_2.output"
+    ```
+
+## See also
+
+- [Specializing enum conversion](../../features/enum_conversion.md)
+
+## Version history
+
+Added in version 3.4.0.