It confuses people that both `--no-fail-fast` and `--keep-going` exist
on `cargo test` and `cargo bench` but with slightly different behavior.
The intended use cases for `--keep-going` involve build commands like
`build`/`check`/`clippy` but never `test`/`bench`.
Hence, this commit removes `--keep-going` from `test`/`bench` and
provides guidance of `--no-fail-fast` instead.
If people really want to build as many tests as possible, they can also
do it in two steps:
cargo build --tests --keep-going
cargo test --test --no-fail-fast
This mirrors some of the categories from `cargo help` (the man pages).
There are fewer categories to avoid extra vertical space. Instead, they
are left int the `Options` category but put first.
