Add type hints

[barneygale]

Per justindujardin/pathy#105 (comment)

[barneygale]

To annotate PathBase.stat() we'll need to address #3

[ap--]

Hi @barneygale,

I finally found some time to start moving universal_pathlib to PathBase. To make some of the type checks pass, I wrote type stubs for parts of pathlib_abc. If you're interested I could make a PR here, and upstream them.

The problem is of course, that the type information has to be kept up-to-date separately.

see: https://github.com/fsspec/universal_pathlib/pull/270/files#diff-47f26e6dbeda71d5163654c5951783766ee5e48e58d98abc09468cd28aed9539

Cheers,
Andreas