Reorganize directories (#3462)

* 🚚 move files
* 🚚 rename doc folder to docs
* 🚚 rename test folder to tests

docs/mkdocs/docs/api/basic_json/std_swap.md

@@ -0,0 +1,51 @@
+# std::swap<basic_json\>
+
+```cpp
+namespace std {
+    void swap(nlohmann::basic_json& j1, nlohmann::basic_json& j2);
+}
+```
+
+Exchanges the values of two JSON objects.
+
+## Parameters
+
+`j1` (in, out)
+:   value to be replaced by `j2`
+
+`j2` (in, out)
+:   value to be replaced by `j1`
+
+## Possible implementation
+
+```cpp
+void swap(nlohmann::basic_json& j1, nlohmann::basic_json& j2)
+{
+    j1.swap(j2);
+}
+```
+
+## Examples
+
+??? example
+
+    The following code shows how two values are swapped with `std::swap`.
+     
+    ```cpp
+    --8<-- "examples/std_swap.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/std_swap.output"
+    ```
+
+## See also
+
+- [swap](swap.md)
+
+## Version history
+
+- Added in version 1.0.0.
+- Extended for arbitrary basic_json types in version 3.10.5.