GValue: convert [String] <-> GStrv

[QuLogic]

As a followup to #3, I now have a GObject property that is a GStrv (aka gchar **) for which I'd like to pass values in a Swift-like manner. I believe the closest to this would be a [String]. It appears that the GValue converter does not handle any cases of GStrv, either going out from Swift or back to Swift.

For some reason the docs don't show up online, but do appear in devhelp. The docs in the source are here. An example of this in use is the authors property of GtkAboutDialog.

[QuLogic]

Relatedly, the setter for the above example takes UnsafeMutablePointer<UnsafePointer<CChar>?>!, which would be nice to specialize into a [String].