Merge pull request #642 from bvssvni/master

Removed stuff that moved to rust-event
Added `Scene` and `Action`
Merge pull request #644 from Coeuvre/master

Added `Scene` and `Action`
Implemented action `FadeIn`, `FadeOut`, `FadeTo`
Merge branch 'master' of https://github.com/pistondevelopers/piston
Fixed doc
Unified the parameters of `ActionState`
Added `Ease(Rate)In`, `Ease(Rate)Out`, `Ease(Rate)InOut` actions

  Those Ease actions can be combined with interval actions like
  `MoveTo`, `RotateTo` to perform tweening animation.
Merge pull request #645 from Coeuvre/master

Implemented action `FadeIn`, `FadeOut`, `FadeTo`. Added `Ease(Rate)In`, `Ease(Rate)Out`, `Ease(Rate)InOut` actions
Moved code to `sprite`
Merge pull request #646 from Coeuvre/master

Moved code to `sprite`
Updated the dependencies link
Merge pull request #649 from Coeuvre/master

Updated the dependencies link
Updated some details

* Pointed Rust link to rust-lang.org
Added donation table
Added DragController

Closes https://github.com/PistonDevelopers/piston/issues/653