Adds a few tests as well.
…1/4, test note duration with something other than 2 in the denominator, more stringification tests.
… header section yet.
…ection or the tune body.
…fully correct) support for quartuplets and quintuplets.
…gainst the "draft 2.0" ABC grammar we've been working from, but matches the text of the "official" ABC 2.0 standard -- not to mention the Anthony Francis project ABC files.