Add static type hints

[headtr1ck]

Since static typing has come a long way in python, it would be nice if you could add static type hints to netCDF4.

There has already been some work done here: python/typeshed#9545

If you think that this support should be carried out externally (like in the linked typeshed issue), feel free to close this issue.

[jswhit]

there was some work done on this (#1279), but the OP closed the pull request.

[RandallPittmanOrSt]

Hey, @headtr1ck, @jswhit, @Woefie, high five on getting the type stubs into 1.7.2! (ref #1279, #1302, and #1349)! Thanks especially to Lars and Michael for your initial work and Jeff and Michael for your meticulous reviews of my PR. It's been a pleasure to work with you on this.