Missing py.typed #121
Description
The project is very well typed but because of the missing py.typed marker, mypy ignores it when hdwallet types are used on client projects (without the py.typed mypy downgrades all of the library types to Any).
Package maintainers who wish to support type checking of their code MUST add a marker file named py.typed to their package supporting typing.
Would it be possible to add the py.typed marker to the root of the hdwallet package? Happy to raise the PR (it's just an empty file)...