Add py.typed file and distribute it upon installation (#1344)

Author: felixdivo

can/py.typed

@@ -78,6 +78,7 @@
         "": ["README.rst", "CONTRIBUTORS.txt", "LICENSE.txt", "CHANGELOG.md"],
         "doc": ["*.*"],
         "examples": ["*.py"],
+        "can": ["py.typed"],
     },
     # Installation
     # see https://www.python.org/dev/peps/pep-0345/#version-specifiers