Phaser.Tween.from

Added a reverse tweening function that will accept properties of where you want to start the tween from and will end the tween at the current property or properties that are passed in.

Usage:

```language-javascript
var sprite = game.add.sprite(game.world.centerX, game.world.centerY, 'yeoman');
game.add.tween(sprite).from({x: 0 - sprite.width}, 1000, Phaser.Easing.Bounce.Out, true);
```
Input.getPointerFromIdentifier docs update to reflect where the identifier comes from. Pointer properties now set to give it fixed defaults (thanks @JirkaDellOro, #793)
Merge pull request #792 from codevinsky/tween-from

Phaser.Tween.from