Start work on TreeStore
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/gtk/cast.rs
	src/gtk/ffi.rs
Add commented TreeStore functions and change GType from c_int to c_ulong
Fix comment
Add ListStore
Add functions to cast stores to a model
Add GType constants to glib::ffi
Remove duplicate GType definitions
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/gtk/widgets/treeview.rs
Use more specific type for GType arguments
Import only GType for brevity
Allow adding columns to TreeView and start work on ListStore functions
Finish ListStore functions and remove TreeIter wrapper
Add convenience function
Finish TreeStore functions
Use *mut for arguments that can take ptr::null_mut()
Add *mut to a few more places
Revert "Add convenience function"

This reverts commit cf92e8539eca8a7399d84f1b72d9d6aef2fc6f27.
Fix typos
Add treeview example