Automap

This release includes built wheels for CPython 3.6 and 3.7 on all operating systems.

**This release drops support for Python 3.5.** It also reduces the footprint of the mappings by about 25%, meaning that they now take up slightly less memory than the equivalent `dict`, on average. Several deallocation issues for views and iterators have been fixed, and iterators now have a length estimate available via `__length_hint__`.

**This release changes the `keys`, `values`, and `items` methods to return updating view types.** It also adds an `update` method to `AutoMap` for adding multiple new keys in a single expression, adds support for the `reversed` built-in function, and slightly improves performance for keys with lots of hash collisions.

This release adds a new `add` method to `AutoMap`, used for inserting a single new key.

**This release raises a `ValueError` when encountering duplicate keys (previously, a `KeyError` was raised).** It also makes union operations slightly more efficient.

This release fixes a bug in the table resizing logic during updates.