kernel-doc: warn on badly formatted short description

Make kernel-doc warn when a function/struct/union/typedef does not contain
a properly formatted short description, such as:
 * scsi_devinfo: set up the dynamic device list
or
 * scsi_devinfo -

This warning is only generated when verbose (-v) mode is used.

Also explain the -v command line option in the -h output.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>