Reorganize directories (#3462)

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

docs/mkdocs/docs/api/basic_json/std_hash.md

@@ -0,0 +1,32 @@
+# <small>std::</small>hash<nlohmann::basic_json\>
+
+```cpp
+namespace std {
+    struct hash<nlohmann::basic_json>;
+}
+```
+
+Return a hash value for a JSON object. The hash function tries to rely on `std::hash` where possible. Furthermore, the
+type of the JSON value is taken into account to have different hash values for `#!json null`, `#!cpp 0`, `#!cpp 0U`, and
+`#!cpp false`, etc.
+
+## Examples
+
+??? example
+
+    The example shows how to calculate hash values for different JSON values.
+     
+    ```cpp
+    --8<-- "examples/std_hash.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/std_hash.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.
+- Extended for arbitrary basic_json types in version 3.10.5.