Reorganize directories (#3462)

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

docs/mkdocs/docs/api/basic_json/operator_ne.md

@@ -0,0 +1,72 @@
+# <small>nlohmann::basic_json::</small>operator!=
+
+```cpp
+bool operator!=(const_reference lhs, const_reference rhs) noexcept;
+
+template<typename ScalarType>
+bool operator!=(const_reference lhs, const ScalarType rhs) noexcept;
+
+template<typename ScalarType>
+bool operator!=(ScalarType lhs, const const_reference rhs) noexcept;
+```
+
+Compares two JSON values for inequality by calculating `#!cpp !(lhs == rhs)`.
+
+## Template parameters
+
+`ScalarType`
+:   a scalar type according to `std::is_scalar<ScalarType>::value`
+
+## Parameters
+
+`lhs` (in)
+:   first value to consider 
+
+`rhs` (in)
+:   second value to consider 
+
+## Return value
+
+whether the values `lhs` and `rhs` are not equal
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear.
+
+## Examples
+
+??? example
+
+    The example demonstrates comparing several JSON types.
+        
+    ```cpp
+    --8<-- "examples/operator__notequal.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator__notequal.output"
+    ```
+
+??? example
+
+    The example demonstrates comparing several JSON types against the null pointer (JSON `#!json null`).
+        
+    ```cpp
+    --8<-- "examples/operator__notequal__nullptr_t.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator__notequal__nullptr_t.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.