add annotations to python/typeshed

[komuw]

https://github.com/python/typeshed/blob/master/CONTRIBUTING.md

[komuw]

depends on; #78

[mmaney]

Anecdotal memorandum:

While trying to find more useful annotations for the cryptography library, I came across the claim that typeshed was no longer preferred; that one can now distribute even out-of-line hints with a package's normal distribution.