Fix flicker in tutorial.
Update tutorial to use `inViewport` instead of `visible` for object visibility test. Thanks Chris Lau!

- inViewport is broken since moving SpriteObject to the `renderable` property (#176)
Update tutorial for new BitmapFont default alignment.
Ticket #176 : Moved the `floating` and `visible` properties to `me.Renderable` and changed `me.ObjectEntity` to inherit from `me.Renderable'
Ticket #176 : Changed `me.ScreenObject` to inherit from `me.Renderable`
Fix invalid UTF-8 character; fixes build error with SED
Ticket #176: Changed `me.ColorLayer`, `me.ImageLayer`, and `me.TMXLayer` to inherit from `me.Renderable`
Ticket #176: Fix `inViewport` property for `me.Renderable` class
Ticket #176: Fix some property collisions on TMX classes now that they inherit from `me.Renderable`

- Also make other TMX classes inherit from `me.Renderable`
- Fix `inViewport` property
- Change platform example to use `inViewport` to detect falling off the screen, instead of checking object position.
Fix TMXTileset cache.

- This was broken by accessing array references on the prototype chain; every object used the same array references.
- To see the bug in action, load the TMX Tile Map example, and switch to each map in order. When you get to the sewer map, everything will be broken.
Fix a doc comment.
Fix another doc comment
Ticket #8: First commit playing with TexturePacker stuff

not that much for now !
ticket #8 : added a function to create a sprite using the Atlas, and other small improvements

still pretty draft anyway :)
small changes here and there, nothing significant today :(
minor changes
ticket #8: added trimming support
changed the sprite rectangle color to green when debugging is enabled
Added more details on the `anchorPoint` property usage + fixed indentation
ticket #8 : use the entity anchor point to define the renderable positioning

* default position is now around the entity center
* platformer example update to bottom aligned (0.5, 1.0) the sprite to
the entity