Transaction library on top of Node-postgres

[golergka]

We've been using Node-postgres for quite a while, but we've ran into a class of subtle use-after-release bugs with it, and I've written a transaction library that fixes this issue: https://github.com/golergka/pg-tx

Would it be okay to add a link to it in the documentation? I suspect that it can help a lot of other folks with these kind of issues.