debug crit option

[mcandre]

-d / --debug:

• Display crit root artifact directory path
• Display the commands that we shell out to
• List enabled targets
• Inherit stdout handles for cross child processes

Not to be confused with cargo build's debug mode.

May be worth renaming the old -v short version flag to -V (uppercase), and adopting -v / --verbose as the name of this feature. That would alleviate some confusion about crit debug logging versus cross / cargo build debug mode.

Alternatively, emit the junk by default, and introduce a -q / --quiet flag, and invite the user to alias crit as crit -q. Though I'm personally not a fan of apps that are too noisy by default.