Mention sortable.js license (MIT) in doc/license.

Thanks-to: Stephen Gordon <stephen.a.gordon@gmail.com>
Rename doc files to uppercase for consistency.
Add example invocations to documentation

Signed-off-by: Heikki Hokkanen <hoxu@users.sf.net>
RHBZ#962168 - Add support for -h/--help options.

In response to user request added support for invoking with the -h or
--help argument to print usage information. Previously usage was only
printed if the user provided less than two arguments AND did not provide
any invalid arguments, as they were unhandled the commonly used -h and
--help arguments counted as invalid.

https://bugzilla.redhat.com/show_bug.cgi?id=962168