From now on, any changes to the help texts will be visible in PR diffs,
which will make it very easy to review, and very hard to accidentally
miss changes to help texts.
If a contributor makes a change to help texts, the `cargo test` failure
text they will see contains instructions on how to update the blessed
help texts:
error: expect test failed
--> ../doc/long-help.txt
You can update all `expect!` tests by running:
env UPDATE_EXPECT=1 cargo test
In short, to update blessed help texts, one simply does
env UPDATE_EXPECT=1 cargo test
Do not run the tests if the `git` feature is missing, since then
`--diff` will be missing from `--help`. And do not run the tests on
Windows, because then the help text will contain the term `.exe`.
Move man page step to after cargo doc step so that the man page exists
when we look for it.
