Fix __init__ to allow for proper package use (#491)

Prior to this, __init__ running would merely create an empty module named `openlocationcode` with no attributes on Python 3.10 and 3.9. I haven't tested if this explicitly works on 3.8 and older, but it should.

Co-authored-by: Doug Rinckes <drinckes@google.com>

python/openlocationcode/__init__.py

@@ -1 +1,4 @@
-from openlocationcode import *
+if __name__ == "__main__":
+    from openlocationcode import *
+else:
+    from .openlocationcode import *