Use `bifurcate` instead of `rusty-fork`

rusty-fork was great to get assay working but it has a few problems:

• It's not maintained
• It can't handle ?
• Inter process communication isn't the greatest
• Handling failures could be better

I've decided to make a crate bifurcate that does this from the ground up.

bifurcate is not public, I would be very interested in a rusty fork alternative