[v0.1] Fix warnings and test dates (#209)

Zero changes to functionality, just ensures that everything will
continue to work if new contributions come in.

* CI: downgrade cfg-if for Rust 1.21
* Use `?` instead of the deprecated `try!`
* Allow ellipsis_inclusive_range_patterns
* Allow deprecated ONCE_INIT
* Allow deprecated trim_left_matches
* Set SOME_FUTURE_DATE to Y2038
* Allow deprecated Error::description
* Switch to GitHub workflows
* Update README.md badges
* Generate the lock file before downgrading
* Allow more deprecations on macos and windows
* Update windows use of TOKEN_PRIVILEGES
* Remove outdated badges

Co-authored-by: Jacob Pratt <the.z.cuber@gmail.com>