Please do fork this project and issue Pull Requests. There are two caveats though:
First, there are some philosophic goals at play here, mainly around making computer encryption software easy to use, which is deceptively difficult. I don't like rejecting Pull Requests, but additions that run counter to those goals won't be accepted. If you're not sure, add an issue before starting work.
Second, as part of the above, this project is in the public domain. I retain no rights to how it's used. Your Pull Request constitutes your good faith contribution of the work therein into the public domain as well. I don't think that will really be a problem for most people, but you should know that going in. To simplify matters though, please include a --clearsign'd version of WAIVER.txt into waivers/
gpg --output waivers/<yourname>.asc --clearsign WAIVER.txt