Consolidate documentation (#3071)

* 🔥 consolidate documentation
* ♻️ overwork std specializations
* 🚚 move images files to mkdocs
* ♻️ fix URLs
* 🔧 tweak MkDocs configuration
* 🔧 add namespaces
* 📝 document deprecations
* 📝 document documentation generation
* 🚸 improve search
* 🚸 add examples
* 🚧 start adding documentation for macros
* 📝 add note for https://github.com/nlohmann/json/issues/874#issuecomment-1001699139
* 📝 overwork example handling
* 📝 fix Markdown tables

doc/mkdocs/docs/api/basic_json/is_structured.md

@@ -1,4 +1,4 @@
-# basic_json::is_structured
+# <small>nlohmann::basic_json::</small>is_structured
 
 ```cpp
 constexpr bool is_structured() const noexcept;
@@ -18,6 +18,15 @@ No-throw guarantee: this member function never throws exceptions.
 
 Constant.
 
+## Possible implementation
+
+```cpp
+constexpr bool is_primitive() const noexcept
+{
+    return is_array() || is_object();
+}
+```
+
 ## Notes
 
 The term *structured* stems from [RFC 8259](https://tools.ietf.org/html/rfc8259):
@@ -27,7 +36,7 @@ The term *structured* stems from [RFC 8259](https://tools.ietf.org/html/rfc8259)
 
 Note that though strings are containers in C++, they are treated as primitive values in JSON.
 
-## Example
+## Examples
 
 ??? example
 
@@ -43,6 +52,12 @@ Note that though strings are containers in C++, they are treated as primitive va
     --8<-- "examples/is_structured.output"
     ```
 
+## See also
+
+- [is_primitive()](is_primitive.md) returns whether JSON value is primitive
+- [is_array()](is_array.md) returns whether value is an array
+- [is_object()](is_object.md) returns whether value is an object
+
 ## Version history
 
 - Added in version 1.0.0.