Pr 183 w/ master merged

This is #183, with master merged in, and with qless-core updated to the latest.

I'm going to review this and the qless-core PRs some more and then hopefully merge here in a bit.
If no max value is set, this will return a `0`, which implies that it will let no jobs through, whereas `nil` would mean that there is no max.

Is the `to_i` necessary or can this return `nil`?