Add __version__ attribute to package

src/betterproto/__init__.py

@@ -24,6 +24,7 @@ from typing import (
 )
 
 from ._types import T
+from ._version import __version__
 from .casing import camel_case, safe_snake_case, snake_case
 from .grpc.grpclib_client import ServiceStub
 

src/betterproto/_version.py

@@ -0,0 +1,3 @@
+from pkg_resources import get_distribution
+
+__version__ = get_distribution("betterproto").version