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/string_t.md

@@ -1,4 +1,4 @@
-# basic_json::string_t
+# <small>nlohmann::basic_json::</small>string_t
 
 ```cpp
 using string_t = StringType;
@@ -45,6 +45,22 @@ This implementation is interoperable as it does compare strings code unit by cod
 String values are stored as pointers in a `basic_json` type. That is, for any access to string values, a pointer of type
 `string_t*` must be dereferenced.
 
+## Examples
+
+??? example
+
+    The following code shows that `string_t` is by default, a typedef to `#!cpp std::string`.
+     
+    ```cpp
+    --8<-- "examples/string_t.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/string_t.output"
+    ```
+
 ## Version history
 
 - Added in version 1.0.0.