POSIX, options, usage, test

I made the script POSIX compliant and tested it with dash. Added options to configure the final output and allow inclusion of the `includeSubDomains` and `report-uri` directives. I created a test as well that checks the final output of the script. Finally I changed the license information in the source files and the `README` to comply with the recommendations from the [Creative Commons Wiki](https://wiki.creativecommons.org/CC0_FAQ#May_I_apply_CC0_to_computer_software.3F_If_so.2C_is_there_a_recommended_implementation.3F).

Thanks for your script and the idea for it.