generate ibuffer filter groups from eproject info

[dcrewi]

[jrockway]

Doesn't this kind of feel more like an ibuffer feature than an eproject feature? It should be easy to pick any filter to toggle on and off with a key-binding; not just eproject.

I'd appreciate it if you opened a bug in the eproject issue tracker noting that we should try to push this feature upstream and add a ;;; TODO(dcrewi) comment with the link to the issue and a description. Then I will merge this PR and hopefully we will remember to talk to the ibuffer folks and see if we can push a more generic mechanism upstream.

As always, thanks very much for your patch!