[installer] Group support added for Development Pods mirroring the folde...

Hopefully fixes https://github.com/CocoaPods/CocoaPods/issues/2145 by adding a group support for development pods.
It reflects the filesystem structure using subgroups under Development Pods group, thus eases the pod development in tandem with a host application.

Similar complain here: http://stackoverflow.com/questions/21168826/preserve-folder-structure-cocoa-pods and here: https://github.com/CocoaPods/CocoaPods/issues/648


I see. This makes total sense. Can you adjust the doc slightly to reflect this more clearly? E.g.

> Wether the file is part of a development pod.
> If it is then a group structure is created that reflects the structure on the file system. Where needed, intermediate groups are created, similar to how `mkdir -p` operates.

PS Also maintain the 80 chars max width for lines ;)