chisel restart should probably restart the process

[espindola]

I just sent a pull request for restarting deno. That works, but convinced me that our restart infrastructure is too complicated. We should probably really restart the process using nix::unistd::execv or just exit and have chisel start a new chiseld.

A big advantage is that we would be able to use Once or lazy_static. We would also not need to worry about complications around restarting deno with futures pending that are using the old one.