New crates.io versions available and API improvements

TLDR: A lot of minor adds/fixes once again. Few API improvements but the most important ones are:

• Add even more properties (both “normal” and children ones).
• Add of Into<T> for every nullable types.

Changes §

For the interested ones, here is the list of the (major) changes:

Gtk:

• Add child properties for Notebook
• Add child properties for Box
• Add basic drag and drop support

Gdk:

• Fix RGBA
• Generate Gdk classes
• Add GdkAtom
• Add GdkAtom part 2

Sys:

• Use FFI types for constants, string ends with ‘/0’, bitflags update and make all struct fields public, etc

GLib:

• Fix array of string for full transfer
• Convert string constants from FFI
• Directly access the GType in the GValue instead of doing raw pointer casting
• Add support for getting a &str from a GValue without copying

Gio:

• Generate interface functions

Cairo:

• Add scaled font
• Add proper glib bindings for font types
• Make glib dependency optional

Pango:

• Generate more enums and objects

Thanks to all of ours contributors for their (awesome!) work for this release:

• @EPashkin
• @Susurrus
• @antoyo
• @sdroege
• @johncf
• @rtsuk
• @GuillaumeGomez