This creates distinct tutorial examples from complex feature examples
(more how-tos). Both sets are getting builder / derive versions (at
least the critical ones).
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"
This reverts commits 24cb8b1..d0abb37 from clap-rs/clap#1840
This is part of #16. clap-rs/clap#1840 wasn't the right call but we
don't have time to make the decision now, so instead of having one
option and changing it in 4.0, this reverts back to clap2 behavior.
Improved printing instead of printing out the `Vec` using `{:?}`,
`join(", ")` for improved printing. Improved documentation to b emore
explicit and apply to removal of `FlagSubCommand` -> `App::short_flag`
and `App::long_flag`
Instead of a `FlagSubCommand` struct the addition of two simple methods
to `App`. `App::long_flag` and `App::short_flag` that cover all the
bases of the many methods that were provided in `FlagSubCommand`. This
API is far simpler to use and more akin to the present `Arg::long` and `Arg::short`.
