feat: add ability to get command information from *State

[mfridman]

I currently handle retrieving flags (or env variables) from my application. I am able to print out something like:

error: must provide --dir flag or set DIR environment variable

However, it'd be nice if the command name could be printed so the error looks something like this (notice the extra command information):

error: command "goose status": must provide --dir flag or set DIR environment variable

This is currently not possible because path []*Command is unexported on the *State, and that object is the only thing available in Exec functions. We should consider exporting it, or adding a method to retrieve either the full command path or just the terminal command.