rust-cli

We may not want to emit colors when the input is not a TTY. E.g., when redirecting the output to a file. I think we should add a switch to force usage of color, though. There is also NO_COLOR, though off hand I am not convinced that we need to follow it.

The environment variable $XSHE_FILE should be able to set where xshe checks for its configuration file if none of the flags -p, -t, or -f are set.

Right now, the program checks locations in this order:

• $XDG_CONFIG_HOME/xshe.toml, if $XDG_CONFIG_HOME is set.
• ~/.config/xshe.toml.

The desired behavior is add the following check before the other 2:

• $XSHE_FILE, if `$XSH