Drop support for old python versions and add type annotations

[stevearc]

Fixes #422

Dropping support for python 3.5 and earlier (3.5 reached end-of-life September 5, 2020)

This adds coverage for most of the public API, but there are still some areas that aren't covered yet.

• script_host.py is ignored entirely
• host.py is ignored entirely
• the msgpack_rpc submodule has partial coverage
• there are some Any annotations sprinkled around on some of the more complex functions

I recommend reviewing the commits in order

[lgtm-com[bot]]

This pull request introduces 2 alerts when merging 7e89d6a836c9f12a72370f78ef1643d5681101b4 into 581cba4fe027b4e02619ad69cc672c742e45cce1 - view on LGTM.com

new alerts:

• 2 for `__init__` method calls overridden method

[lgtm-com[bot]]

This pull request introduces 2 alerts when merging fdc5c560de18cfa061b08ccfa680bd4c7faf3034 into 581cba4fe027b4e02619ad69cc672c742e45cce1 - view on LGTM.com

new alerts:

• 2 for `__init__` method calls overridden method

[bfredl]

In general I agree with this, but I would suggest for this PR to only drop obsolete python version support, and adding annotations to existing methods where we find that useful. We should consider adding more wrapper methods (and to what detail we want to specify those) in a separate follow-up PR.

[stevearc]

Sounds good to me! I'll force push this PR to remove the extra wrapper methods

[lgtm-com[bot]]

This pull request introduces 2 alerts when merging 77b0616a6f907c2f707e10b6a41125c6e0733e4b into 581cba4fe027b4e02619ad69cc672c742e45cce1 - view on LGTM.com

new alerts:

• 2 for `__init__` method calls overridden method

[lgtm-com[bot]]

This pull request introduces 2 alerts when merging b17943aa0361216f6f6b37c18a96db9ce9d1af62 into 71102c03efdcd6e7a1db1057a68478fc2249734d - view on LGTM.com

new alerts:

• 2 for `__init__` method calls overridden method

[cbrxyz]

This PR is awesome! Any way this can be reviewed/merged?

[benjamin-kirkbride]

Any update on getting this merged?

[justinmk]

Rebased. https://github.com/neovim/pynvim/pull/526 resurrected CI but Windows tests are currently broken. That's unrelated to this PR so doesn't block this PR.