Use `Optional` type hints where appropriate (#168)

+ Belatedly `make format`
+ Convenience: bump version to 2.1.3 for release

Bump version to 2.1.2 for release (#166)

Bump version to 2.1.1 for release (#164)

Bump version to 2.1.0 (#146)

Bump version to 2.0.0 (#139)

+ Improve `max_results`/`delay_seconds` types, defaults (#138)
+ Eliminate `get`, deprecate `Search.Results` (#137)
+ Accelerate CI integration tests (#140)

Replace `/` with `_` in legacy-format IDs in download filenames (#118)

Fixes #117. Differentiates character-escaping strategies for paper
titles and paper IDs:

+ IDs: only replace `/` with `_`, to account for legacy-form IDs.
+ Titles: replace non-word (i.e. `[^\w]`) characters with `_`.

Adds a regression test.

Indicate Python version in trove classifiers (#112)

Concession to get the Shields.io badge to work. `python_requires`
doesn't cut it: badges/shields#5550

Increment patch version to allow PyPI release: 1.4.7.

Set python_requires >=3.7 (#111)

Should capture what we test in CI: 3.7, ..., 3.10, 3.11. Increment the
version to 1.4.6 to reflect a patch: this isn't a breaking change for
any of the supported versions.

Update README.md version badge to resolve supported versions from PyPI.

Disambiguate generic `list` type hints (#109)

* Disambiguate generic list types

Also updates string annotations in constructor arguments.

Imports `annotations` from `__future__`, which allows referring to
class types before they're defined.

Verification: searched for all instances of `: list`; there aren't any
left in arxiv.py. Generated docs look good.

* Increment version for patch

Fix docstring: `updated` and `published` are datetimes (#107)

* Bump package version to 1.4.4

* Fix docstring: updated and published are datetimes (#106)

See `_from_feed_entry` and `_to_datetime`: auto-converting struct_time to datetimes. Update the docstring to reflect the conversion.

* Pin pyenv Python version 3.10.4

* Bump pdoc to 13.1.0; log pdoc version before generating docs

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Co-authored-by: Nasy <nasyxx@gmail.com>