Made an enum GtkWrapBoxPacking for the expand/fill horizontal/vertical boolean options... changed xpadding/ypadding to be horizontal-padding and vertical-padding for a more consistent api and better readablility.
Ammended documentation for GTK_WRAP_BOX_SPREAD_EVEN and renamed GTK_WRAP_BOX_SPREAD_BEGIN -> GTK_WRAP_BOX_SPREAD_START.
Some coding style cleanups, rename Priv to Private, add docs
