Remove positional arguments in favor of getopts

This patch adds getopts based short options and removes
positional arguments.

Mandatory option -r COMMONNAME (cs**R**equest).
Certificate data may be supplied optionally using arguments.

Add -h option for a brief usage.

Certificate key/requests are now dropped to a sub-directory
data/ which is subject to .gitignore.
Merge pull request #1 from spul/master

Remove positional arguments in favor of getopts