Reorganize directories (#3462)

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

docs/mkdocs/docs/api/basic_json/object_t.md

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+# <small>nlohmann::basic_json::</small>object_t
+
+```cpp
+using object_t = ObjectType<StringType,
+                            basic_json,
+                            default_object_comparator_t,
+                            AllocatorType<std::pair<const StringType, basic_json>>>;
+```
+
+The type used to store JSON objects.
+
+[RFC 8259](https://tools.ietf.org/html/rfc8259) describes JSON objects as follows:
+> An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a
+> string, number, boolean, null, object, or array.
+
+To store objects in C++, a type is defined by the template parameters described below.
+
+## Template parameters
+
+`ObjectType`
+:   the container to store objects (e.g., `std::map` or `std::unordered_map`)
+
+`StringType`
+:   the type of the keys or names (e.g., `std::string`). The comparison function `std::less<StringType>` is used to
+    order elements inside the container.
+
+`AllocatorType`
+:   the allocator to use for objects (e.g., `std::allocator`)
+
+## Notes
+
+#### Default type
+
+With the default values for `ObjectType` (`std::map`), `StringType` (`std::string`), and `AllocatorType`
+(`std::allocator`), the default value for `object_t` is:
+
+```cpp
+// until C++14
+std::map<
+  std::string, // key_type
+  basic_json, // value_type
+  std::less<std::string>, // key_compare
+  std::allocator<std::pair<const std::string, basic_json>> // allocator_type
+>
+
+// since C++14
+std::map<
+  std::string, // key_type
+  basic_json, // value_type
+  std::less<>, // key_compare
+  std::allocator<std::pair<const std::string, basic_json>> // allocator_type
+>
+```
+
+See [`default_object_comparator_t`](default_object_comparator_t.md) for more information.
+
+#### Behavior
+
+The choice of `object_t` influences the behavior of the JSON class. With the default type, objects have the following
+behavior:
+
+- When all names are unique, objects will be interoperable in the sense that all software implementations receiving that
+  object will agree on the name-value mappings.
+- When the names within an object are not unique, it is unspecified which one of the values for a given key will be
+  chosen. For instance, `#!json {"key": 2, "key": 1}` could be equal to either `#!json {"key": 1}` or
+  `#!json {"key": 2}`.
+- Internally, name/value pairs are stored in lexicographical order of the names. Objects will also be serialized (see
+  [`dump`](dump.md)) in this order. For instance, `#!json {"b": 1, "a": 2}` and `#!json {"a": 2, "b": 1}` will be stored
+  and serialized as `#!json {"a": 2, "b": 1}`.
+- When comparing objects, the order of the name/value pairs is irrelevant. This makes objects interoperable in the sense
+  that they will not be affected by these differences. For instance, `#!json {"b": 1, "a": 2}` and
+  `#!json {"a": 2, "b": 1}` will be treated as equal.
+
+#### Limits
+
+[RFC 8259](https://tools.ietf.org/html/rfc8259) specifies:
+> An implementation may set limits on the maximum depth of nesting.
+
+In this class, the object's limit of nesting is not explicitly constrained. However, a maximum depth of nesting may be
+introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the
+[`max_size`](max_size.md) function of a JSON object.
+
+#### Storage
+
+Objects are stored as pointers in a `basic_json` type. That is, for any access to object values, a pointer of type
+`object_t*` must be dereferenced.
+
+#### Object key order
+
+The order name/value pairs are added to the object is *not* preserved by the library. Therefore, iterating an object may
+return name/value pairs in a different order than they were originally stored. In fact, keys will be traversed in
+alphabetical order as `std::map` with `std::less` is used by default. Please note this behavior conforms to
+[RFC 8259](https://tools.ietf.org/html/rfc8259), because any order implements the specified "unordered" nature of JSON objects.
+
+## Examples
+
+??? example
+
+    The following code shows that `object_t` is by default, a typedef to `#!cpp std::map<json::string_t, json>`.
+     
+    ```cpp
+    --8<-- "examples/object_t.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/object_t.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.