Reorganize directories (#3462)

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

docs/mkdocs/docs/api/json_pointer/push_back.md

@@ -0,0 +1,39 @@
+# <small>nlohmann::json_pointer::</small>push_back
+
+```cpp
+void push_back(const string_t& token);
+
+void push_back(string_t&& token);
+```
+
+Append an unescaped token at the end of the reference pointer.
+
+## Parameters
+
+`token` (in)
+:   token to add
+
+## Complexity
+
+Amortized constant.
+
+## Examples
+
+??? example
+
+    The example shows the result of `push_back` for different JSON Pointers.
+     
+    ```cpp
+    --8<-- "examples/json_pointer__push_back.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/json_pointer__push_back.output"
+    ```
+
+## Version history
+
+- Added in version 3.6.0.
+- Changed type of `token` to `string_t` in version 3.11.0.