Display any error returned by main in a nicer way

[nickwanninger]

Previously, returning an error from main prints out the rust representation of the error struct:

This PR moves the existing main into it's own function so the real main can handle errors nicely:

[Mart-Bogdan]

I mean other code is having this check:

    let color_choice = if atty::is(Stream::Stdout) {
        ColorChoice::Auto
    } else {
        ColorChoice::Never
    };
    let stdout = BufferWriter::stdout(color_choice);