Auto merge of #3614 - matklad:simpler-cli-2, r=alexcrichton

Remove generic infrastrucure for printing json

Only a couple of command really use this features, so it's clearer just to print json right on the spot rather then return it though the call stack.

`CliResult` is now just a `Result<(), CliError>`.

diff --cc src/bin/new.rs
Simple merge