In particular, rename
- libraries to lib*-3.0.so
- pc files to *-3.0.pc
- include paths to /usr/include/gtk-3.0/*
- module paths to /usr/lib/gtk-3.0/*
- rc files names to gtk-3.0/gtkrc
- commandline utilities to *-3.0
- adjust documentation
Also change the install location for unix-print headers to
/usr/include/gtk-3.0/unix-print/gtk.
