Marcel, the pythonic shell, now has workspaces

Marcel had its 15 seconds of fame here on HN a few weeks ago: https://news.ycombinator.com/item?id=37991746

I've added workspaces to marcel. A workspace provides for a per-project persistent command history, environment variables, and a per-project startup script. The new features are briefly described here: https://www.marceltheshell.org/workspaces