Reorganize directories (#3462)

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

docs/mkdocs/docs/api/json_pointer/empty.md

@@ -0,0 +1,39 @@
+# <small>nlohmann::json_pointer::</small>empty
+
+```cpp
+bool empty() const noexcept;
+```
+
+Return whether pointer points to the root document.
+
+## Return value
+
+`#!cpp true` iff the JSON pointer points to the root document.
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Constant.
+
+## Examples
+
+??? example
+
+    The example shows the result of `empty` for different JSON Pointers.
+     
+    ```cpp
+    --8<-- "examples/json_pointer__empty.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/json_pointer__empty.output"
+    ```
+
+## Version history
+
+Added in version 3.6.0.