This ports our example testing over to [trycmd](https://docs.rs/) so
we can:
- More thoroughly test our examples
- Provide always-up-to-date example usage
The old way of testing automatically picked up examples. This new way
requires we have a `.md` file that uses the example in some way.
Notes:
- Moved overall example description to the `.md` file
- I added cross-linking between related examples
- `14_groups` had a redundant paragraph (twice talked about "one and
only one"
Since usage parser and yaml are on the way to being deprecated (#8, #9),
doing a rename also seems excessive, so rolling it back.
Past relevant PRs:
- clap-rs/clap#1157
- clap-rs/clap#1257
- Manually fix some problems
- Run 'cargo fix --clippy'
Commits taken from similar PRs open at that time:
- Replace indexmap remove with swap_remove
Resolves#1562 and closes#1563
- Use cognitive_complexity for clippy lint
Resolves#1564 and closes#1565
- Replace deprecated trim_left_matches with trim_start_matches
Closes#1539
Co-authored-by: Antoine Martin <antoine97.martin@gmail.com>
Co-authored-by: Brian Foley <bpfoley@users.noreply.github.com>
