Add automated unit tests
The ideal test for Styliner is to render inlined and non-inlined versions of complex pages in a browser, and make sure that the applied styles are identical. (see tests/TestServer.js) This requires a browser with a full CSS stack to test against; I'll use PhantomJS for that.
Without this, no one can contribute. Really sad.
Yes; the problem is that such tests aren't so simple to write, and I don't have time to write them. If you want to write them yourself, I'd welcome that.
Also note that now that Gmail supports CSS, this project should no longer be necessary.
Not all Gmail products support CSS yet, though: https://litmus.com/blog/gmail-to-support-responsive-email-design/
This project still has at least a few months left. Also, who knows what the future holds.