Add support for letting the generators save multiple files.
Add support for letting the generators save multiple files.

For what I was doing with the PkgConfig generator I had to
be able to generate one file per dependency. The current
generator system was not able to handle this. Fortunately
it was a easy change without having to break any current
generators.

memsharded/conan,dragly/conan,birsoyo/conan,memsharded/conan,luckielordie/conan,memsharded/conan,mropert/conan,dragly/conan,conan-io/conan,lasote/conan,mropert/conan,tivek/conan,birsoyo/conan,lasote/conan,luckielordie/conan,Xaltotun/conan,memsharded/conan,Xaltotun/conan,tivek/conan,conan-io/conan,conan-io/conan