`create_kernel` API Update

To reduce the kwargs hell, we introduced dataclasses, which handle the settings of create_kernel and similar functions. In addition we introduced type-hints for the API functions to increase usability and simplify development.

pystencils/kernel_decorator.py

 import ast
 import inspect
 import textwrap
-from typing import Callable, Union
+from typing import Callable, Union, List, Dict
 
 import sympy as sp
 
@@ -11,7 +11,7 @@ from pystencils.sympyextensions import SymbolCreator
 __all__ = ['kernel']
 
 
-def kernel(func: Callable[..., None], return_config: bool = False, **kwargs) -> Union[list[Assignment], dict]:
+def kernel(func: Callable[..., None], return_config: bool = False, **kwargs) -> Union[List[Assignment], Dict]:
     """Decorator to simplify generation of pystencils Assignments.
 
     Changes the meaning of the '@=' operator. Each line containing this operator gives a symbolic assignment