add easy and performant way to have project status in shell prompt about travis.rb

[sarahhodne]

We could cache by current commit SHA here? This would break down if we restart a job, thought.

[rkh]

Right. We could also have a background process write the state somewhere.

[rkh]

Do we want it to display the latest build or the status of the currently checked out commit? Because for the first one (which would be easier and reliable to implement) the caching wouldn't work that well...

[sarahhodne]

Right. I've tried looking into adding caching to Travis Lite as well, and it's not easy, seeing as things change a lot.

Could we latch onto the pusher feed in a background process?

[rkh]

That's what I was thinking. I was playing with the idea of adding pusher support to the library anyways (see #15), but I'm not sure how much hassle that would be.

[rkh]

General HTTP caching can be done via ETags, btw, but you'd still need one HEAD request for checking if the cache is fresh. Given that on some setups it might not even be acceptable to fire off a new Ruby process for displaying something in the prompt, I don't think that's an option, though.

[rkh]

I think this is unrealistic with our current performance.