* guix/import/gem.scm: (rubygems-fetch, gem->guix-package)
(gem-recursive-import): Fix to fetch the specified version of the gem.
* guix/scripts/import/gem.scm (show-help): Update the help message.
(guix-import-gem): Modify so the version number to be passed to subsequent
procedures.
* tests/gem.scm: Add tests.
* doc/guix.texi (Invoking guix import): Document.
Signed-off-by: Christopher Baines <mail@cbaines.net>
