Have subscribe_email.pl use the RESTful API, like the subscription forms do

[justingit]

Perhaps subscribe_email.pl ( https://github.com/justingit/dada-mail/blob/master/dada/extras/scripts/subscribe/subscribe_email.pl ) is a little too close to the metal, and should use the RESTFUL API,

https://dadamailproject.com/d/features-restful_web_services.pod.html

like the subscription forms of Dada Mail actually do. This has the benefit of being able to locate the subscribe_email.pl script wherever you'd like, which helps with upgrading. We can also produce examples in other languages other than Perl, as the API isn't tied to that language. I'm also worried that this script is severely outdated - it seems to work, but may fail in surprising ways.