feature-request: target-dir attribute support for source-file element, for iOS

[shazron]

Right now if you install N plugins, all of them are installed in a flat hierarchy in the Plugins group in your project, in Xcode, which is messy.

Specifying a "target-dir" attribute would create a group (or subgroups) that the file would reside under - under the "Plugins" main group.

[alunny]

Good idea - groups are a bit tricky though (inasmuch as I've never created one with node-xcode before). I'm sure it's doable though.