Add an AHOY_COMMAND environment variable to each running command

[hanoii]

This is so that one could maybe use that to know if it was run through ahoy or not.

I have a lot of scripts that I normally wrap around ahoy and I do this to show different helper usage if run from ahoy or directly.

[ocean]

@hanoii Do you mean that the AHOY_COMMAND env var will hold the name of the ahoy subcommand that is currently running, and be passed through into the env vars of the thread that is running the command? Or that the AHOY_COMMAND env var is just set to something like "true" to indicate that this command / set of commands is being run by / within ahoy ??