📝 add more API documentation

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

@@ -0,0 +1,65 @@
+# basic_json::exception
+
+```cpp
+class exception : public std::exception;
+```
+
+This class is an extension of [`std::exception`](https://en.cppreference.com/w/cpp/error/exception) objects with a
+member `id` for exception ids. It is used as the base class for all exceptions thrown by the `basic_json` class. This
+class can hence be used as "wildcard" to catch exceptions, see example below.
+
+```plantuml
+std::exception <|-- json::exception
+json::exception <|-- json::parse_error
+json::exception <|-- json::invalid_iterator
+json::exception <|-- json::type_error
+json::exception <|-- json::out_of_range
+json::exception <|-- json::other_error
+
+interface std::exception {}
+
+class json::exception #FFFF00 {
+    + const int id
+    + const char* what() const
+}
+
+class json::parse_error {
+    + const std::size_t byte
+}
+```
+
+Subclasses:
+
+- `parse_error` for exceptions indicating a parse error
+- `invalid_iterator` for exceptions indicating errors with iterators
+- `type_error` for exceptions indicating executing a member function with a wrong type
+- `out_of_range` for exceptions indicating access out of the defined range
+- `other_error` for exceptions indicating other library errors
+
+## Member functions
+
+- **what** - returns explanatory string
+
+## Member variables
+
+- **id** - the id of the exception
+
+## Example
+
+??? example
+
+    The following code shows how arbitrary library exceptions can be caught.
+    
+    ```cpp
+    --8<-- "examples/exception.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/exception.output"
+    ```
+
+## Version history
+
+- Since version 3.0.0.