rust-dependencies: switch from `users` to `whoami`
`users` is unmaintained, with the maintainer apparently MIA. `whoami` is a
popular crate that does simple wrapping of platform-specific calls.
This makes the overhead from using `blackbox` lower. It used to be up 10ms
on slower hardware for both calls, now down to <1ms which is always good.
Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:
http://docutils.sourceforge.net/rst.html
It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:
http://docutils.sourceforge.net/
Use the Makefile in this directory to generate the man and HTML pages.