Merge pull request #131 from GuillaumeGomez/master

New widget : ToolItemGroup
use namespaced enum, stop reexporting mods containing enums, enums mod is no more public.
fix build with last PR
Update events.rs
Merge pull request #136 from jeremyletang/enums

use namespaced enum
add forgotten traits in rgtk.rs + reorder
rebase
renames all traits to remove possible conflict, and facilitate code comprehension
fix exemple build
Merge pull request #138 from jeremyletang/clean-code

Clean code
Add new widget : SizeGroup