`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/llvm/kernelcreation.py

@@ -26,7 +26,7 @@ def create_kernel(assignments, function_name="kernel", type_info=None, split_gro
 
     :return: :class:`pystencils.ast.KernelFunction` node
     """
-    if target == Target.LLVM:
+    if target == Target.CPU:
         from pystencils.cpu import create_kernel
         code = create_kernel(assignments, function_name, type_info, split_groups, iteration_slice, ghost_layers)
         code._backend = 'llvm'