It can be useful to simply instantiate a Home Manager configuration
without actually building it, for example for the purpose of
pre-building it with some custom command.
PR #1099
This rewrite allows "long options" but unfortunately does not allow
merged options such as `-vn`.
Also improve the home-manager manual page, with this it should include
all sub-commands and arguments.
Finally, include the home-manager manual page in the generated HTML
documentation.
