Replace host_str with "$VIRTUAL_ENV" if exists

[shirok1]

A rough proof of concept. I think this is what #16 talking about.

[Moarram]

I see what you mean. I'd love for ENV to be it's own segment with a dedicated color, but due to the way I've built Headline it's somewhat difficult to add more information segments. However, you've demonstrated that it's easy to modify an existing segment to achieve desired behavior.

To that end, I've just pushed commit c12368a making it even easier to customize the segment data sources by elevating them out of the prompt function so you can set them in ~/.zshrc or wherever. Only downside (and why I didn't do this originally) is that I need to use eval which potentially introduces security concerns that I don't fully understand.

Hopefully this will work reasonably well for you until I can make it easier to add segments