Reorganize directories (#3462)

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

docs/mkdocs/docs/api/json_pointer/back.md

@@ -0,0 +1,40 @@
+# <small>nlohmann::json_pointer::</small>back
+
+```cpp
+const string_t& back() const;
+```
+
+Return last reference token.
+
+## Return value
+
+Last reference token.
+
+## Exceptions
+
+Throws [out_of_range.405](../../home/exceptions.md#jsonexceptionout_of_range405) if JSON pointer has no parent.
+
+## Complexity
+
+Constant.
+
+## Examples
+
+??? example
+
+    The example shows the usage of `back`.
+     
+    ```cpp
+    --8<-- "examples/json_pointer__back.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/json_pointer__back.output"
+    ```
+
+## Version history
+
+- Added in version 3.6.0.
+- Changed return type to `string_t` in version 3.11.0.