Adding Dim3 class

This adds a dim3 class for gpu code and a convenience class decorator for lang.CppClass

src/pystencilssfg/lang/__init__.py

@@ -12,6 +12,7 @@ from .expressions import (
     depends,
     includes,
     CppClass,
+    cppclass,
     IFieldExtraction,
     SrcField,
     SrcVector,
@@ -36,6 +37,7 @@ __all__ = [
     "SrcVector",
     "cpptype",
     "CppClass",
+    "cppclass",
     "void",
     "Ref",
     "strip_ptr_ref",