skytools v3.7

Features:

• config: config_format=2 switches to extended format.
• querybuilder: alt SQL for missing value.
• querybuilder: handle more value types in inline queries.
• querybuilder/plpy: always use prepared plan. Prevously when GD/SD was not given, it switched to inline params, but that was problem because inline value quoting may be different that PL/Python's. Now it always uses plpy.prepare.

Cleanups:

• querybuilder: switch to functools.lru_cache, instead local LRU.
• querybuilder: use regex for parsing, gives cleaner code.
• querybuilder: improve error handling
• natsort: switch to string key, instead of tuple.
• style: Add type annotations to most modules.
• style: use new-style super() everywhere.
• ci: drop win32 repack, abi3 is now supported on win32
• ci: drop ubuntu 16.04, to be obsoleted.
• ci: build wheels using manylinux2014 images.