rhg: add a limited `rhg root` subcommand...
rhg: add a limited `rhg root` subcommand
Clap has been choosen for argument parsing for the following reasons:
- it's a wildly used and maintained crate
- it can deal with OS encoding making it suitable for any encoding
- it supports nonambiguous prefix matching as already available in hg
- it will soon allow for structopts-style declarative pattern instead of the
currently used builder pattern
Differential Revision:
https://phab.mercurial-scm.org/D8613
