Improves mypy config. Adds explicit re-exports to __init__.py.

[Daverball]

mypy --strict will complain if Chameleon does not have explicit re-exports, so as a good citizen of the typing ecosystem we should add them, other people should not have to ignore re-export errors on our behalf. Since the module structure of Chameleon is fairly simple, this shouldn't add any real maintenance burden, since the top-level __init__.py file is the only one that re-exports imported symbols. We can also get rid of the flake8 per-file-ignores for __init__.py this way.

While I was at it I also increased the strictness of the strict config to match mypy --strict, as well as enabled most of the optional warnings. I also added some missing annotations while dealing with the new warn-return-any errors. Once everything is annotated and using the strict config, we can simplify most of the config back down to just strict = true.

[coveralls]

Pull Request Test Coverage Report for Build 8553843913

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 50 of 50 (100.0%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 92.727%

---

Totals
Change from base Build 7753260695:	0.01%
Covered Lines:	3893
Relevant Lines:	4135

---

💛 - Coveralls