Reorganize directories (#3462)

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

docs/mkdocs/docs/api/basic_json/boolean_t.md

@@ -0,0 +1,42 @@
+# <small>nlohmann::basic_json::</small>boolean_t
+
+```cpp
+using boolean_t = BooleanType;
+```
+
+The type used to store JSON booleans.
+
+[RFC 8259](https://tools.ietf.org/html/rfc8259) implicitly describes a boolean as a type which differentiates the two literals
+`#!json true` and `#!json false`.
+
+To store objects in C++, a type is defined by the template parameter  `BooleanType` which chooses the type to use.
+
+## Notes
+
+#### Default type
+
+With the default values for `BooleanType` (`#!cpp bool`), the default value for `boolean_t` is `#!cpp bool`.
+
+#### Storage
+
+Boolean values are stored directly inside a `basic_json` type.
+
+## Examples
+
+??? example
+
+    The following code shows that `boolean_t` is by default, a typedef to `#!cpp bool`.
+     
+    ```cpp
+    --8<-- "examples/boolean_t.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/boolean_t.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.