kngclick: add version option

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
kernelng: slightly better description

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
kernelng: drop unneeded comments

Turns out context_settings propogate automatically to subcommands so
these are not needed.

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>