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/unflatten.md

@@ -1,4 +1,4 @@
-# basic_json::unflatten
+# <small>nlohmann::basic_json::</small>unflatten
 
 ```cpp
 basic_json unflatten() const;
@@ -15,6 +15,10 @@ The function restores the arbitrary nesting of a JSON value that has been flatte
 
 the original JSON from a flattened version
 
+## Exception safety
+
+Strong exception safety: if an exception occurs, the original value stays intact.
+
 ## Exceptions
 
 The function can throw the following exceptions:
@@ -22,10 +26,6 @@ The function can throw the following exceptions:
 - Throws [`type_error.314`](../../home/exceptions.md#jsonexceptiontype_error314) if value is not an object
 - Throws [`type_error.315`](../../home/exceptions.md#jsonexceptiontype_error315) if object values are not primitive
 
-## Exception safety
-
-Strong exception safety: if an exception occurs, the original value stays intact.
-
 ## Complexity
 
 Linear in the size the JSON value.
@@ -36,7 +36,7 @@ Empty objects and arrays are flattened by [`flatten()`](flatten.md) to `#!json n
 their original type. Apart from this example, for a JSON value `j`, the following is always true:
 `#!cpp j == j.flatten().unflatten()`.
 
-## Example
+## Examples
 
 ??? example
 
@@ -52,6 +52,10 @@ their original type. Apart from this example, for a JSON value `j`, the followin
     --8<-- "examples/unflatten.output"
     ```
 
+## See also
+
+- [flatten](flatten.md) the reverse function
+
 ## Version history
 
 - Added in version 2.0.0.