By default, clap only accepts app-level arguments (as opposed to sub-command
level) to be specified before a sub-command: rhg -R ./foo log. Specifying
them after would be rejected: rhg log -R ./foo.
Previously we worked around that by registering global arguments both
at the app level and on each sub-command, but that required looking
for their value in two places. It turns out that Clap has built-in support
for what we want to do, so let’s use it.
Also, Clap "settings" turn out to be either global or not too.
Let’s make AllowInvalidUtf8 apply to sub-commands too.