Standardize the publishing to use the same shell script as the other modules

[SethTisue]

in this repo only, it's handled in build.sbt rather than in a build.sh (as in scala-xml and the other module repos)

it's a pain to maintain this one nonstandard thing

the most recent time I felt the pain was at #394 today, where I wanted to backpublish an existing version for a new Scala version, but lord knows if the custom stuff here allows that

and also just the other day I was talking to @rossabaker who had wanted to contribute a change in this repo that would affect publishing, but he very understandably gave up when he saw the nonstandard setup here

[SethTisue]

pain felt again at #402