Reorganize directories (#3462)

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

docs/mkdocs/docs/api/basic_json/clear.md

@@ -0,0 +1,58 @@
+# <small>nlohmann::basic_json::</small>clear
+
+```cpp
+void clear() noexcept;
+```
+
+Clears the content of a JSON value and resets it to the default value as if [`basic_json(value_t)`](basic_json.md) would
+have been called with the current value type from [`type()`](type.md):
+
+| Value type | initial value        |
+|------------|----------------------|
+| null       | `null`               |
+| boolean    | `false`              |
+| string     | `""`                 |
+| number     | `0`                  |
+| binary     | An empty byte vector |
+| object     | `{}`                 |
+| array      | `[]`                 |
+
+Has the same effect as calling
+
+```.cpp
+*this = basic_json(type());
+```
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear in the size of the JSON value.
+
+## Notes
+
+All iterators, pointers and references related to this container are invalidated.
+
+## Examples
+
+??? example
+
+    The example below shows the effect of `clear()` to different
+    JSON types.
+    
+    ```cpp
+    --8<-- "examples/clear.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/clear.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.
+- Added support for binary types in version 3.8.0.