Merge pull request #126 from GuillaumeGomez/master

TextView widget
add Cargo.lock to .gitignore
implement CellRendererToggle
implement FFIGObject and Clicked signal for TreeViewColumn
Merge pull request #125 from osa1/pr

fix broken GValue setters and make setter methods public
remove unused trait
Merge pull request #127 from osa1/unused_trait

remove unused trait
fail -> panic
Merge pull request #128 from steveklabnik/master

fail -> panic
Update to last rust compiler version (change unused_variable by unused_variables)