Add py.typed file so types can be used for users of mergedeep

[RazerM]

See https://www.python.org/dev/peps/pep-0561/#id18

Without this, mypy won't type check mergedeep in code that uses it as a dependency:

error: Skipping analyzing 'mergedeep': found module but no type hints or library stubs

[WasabiFan]

It looks like this file is in the root of the repo rather than in the mergedeep module folder. Has anyone confirmed that type discovery for this module works right now? Initial indications in my project seem to suggest no.

[sshishov]

For me mypy is complaining actually that this package is not typed

[MicaelJarniac]

Mypy is also telling me that this project is not typed. I do also believe the py.typed file is in the wrong place.

[sshishov]

@clarketm could we please check this? Or do you need any help here?

[TomerGodinger]

Indeed, the py.typed file needs to be inside the mergedeep folder.
It would be nice if it was moved.

Is this library still being maintained? I see the last commits were made three years ago.