Merge pull request #441 from bvssvni/master

Removed 'image_iter.rs'
Merge pull request #443 from bvssvni/master

Removed example 'image.rs'
Merge pull request #445 from bvssvni/master

Removed example 'user_input.rs'
Made `render` and `update` take immutable Args

Closes https://github.com/PistonDevelopers/piston/issues/438
Closes https://github.com/PistonDevelopers/piston/issues/439