Bump python_requires to 3.5.3
Mentioned during sprint today some of the typing constructs we use were not added until Python 3.5.2, specifically typing.Type and typing.DefaultDict and maybe at some point typing.TYPE_CHECKING

https://docs.python.org/3/library/typing.html#typing.Type

This is a bump of the setup files and docs to 3.5.2. 
should change

```
ci/deps/azure-35-compat.yaml:  - python=3.5.*
```

to 3.5.2? Hmm based off error in Linux compat might even need a bump to 3.5.3 per https://github.com/python/typing/pull/267 giving that a look now