Add cache clearing function

For developing purposes it is useful to have a cache-clearing function

pystencils/__init__.py

@@ -8,6 +8,7 @@ from .datahandling import create_data_handling
 from .display_utils import get_code_obj, get_code_str, show_code, to_dot
 from .field import Field, FieldType, fields
 from .config import CreateKernelConfig
+from .cache import clear_cache
 from .kernel_decorator import kernel, kernel_config
 from .kernelcreation import create_kernel, create_staggered_kernel
 from .simp import AssignmentCollection
@@ -27,6 +28,7 @@ __all__ = ['Field', 'FieldType', 'fields',
            'assignment_from_stencil',
            'SymbolCreator',
            'create_data_handling',
+           'clear_cache',
            'kernel', 'kernel_config',
            'x_', 'y_', 'z_',
            'x_staggered', 'y_staggered', 'z_staggered',