Rules only/except, echo mode, macOS

Hey, this is a cool project. I think I'm going to try to make good use of it since local usage of the gitlab runner is no good.

• Do you have any thoughts on doing something with the rules or except/only? I'm often interested in just making sure the right stages run at the right time.
• Would an echo mode make sense where the scripts aren't run but you get the command calls with any environment vars rendered?
• Have you had any issues running this on macOS? I couldn't make it work.