Swap the todo example to the one on todomvc

[chenglou]

Currently the example todomvc is horribly broken. There's already a more feature-complete version on todomvc. I suggest to take it.

[chenglou]

Update: I'll be porting the todomvc example submitted to the actual project to 0.4. Once that's done, we can use that version instead, unless you guys find the example too heavy.

[zpao]

See #307