Added features to Rectangle

- Added top, right, left, bottom
Add flambe.util.Pool.
Add explicit return type.
Add Sprite.pointerIn/pointerOut for rollovers.
Hover event tweaks.
Ensure a pointerMove is always emitted before down and up events.
Merge pull request #226 from Jona85/Added-features-to-Rectangle

Added features to Rectangle
Document the new Rectangle fields.
Add Rectangle.centerX/centerY.
Fix completion in some editors, via @markknol.

Mark says this is still a rare issue, but for now close #216 and
close #220.
Implement stage.lockOrientation() in HTML.

Not implemented in most browsers, but coming soon to Chrome and IE
mobile. Note that you have to be in fullscreen first.

Also should work in Firefox, but fullscreen on mobile is awkward:
https://bugzilla.mozilla.org/show_bug.cgi?id=779324

Closes #4.
Add System.renderer.

Exposes a low-level createTextureFromImage method for creating Flambe
textures from native image data.

Breaking change: System.createTexture and hasGPU have been moved to
System.renderer.
Convert HTML comments to markdown.
Add language hints for dox syntax highlighting.
Documentation formatting.
Update to latest AIR.
initialClone
Enabled the creation of a Library by the means of a Array<Flipbook> rather than Dynamic<Flipbook>. This was done because there was no means of naming each animation through a data-driven pipeline (aka the name had to be hardcoded). I also added a name field to the Flipbook which is now used when creating a Library with Flipbook array
Merge branch 'master' of https://github.com/OvertureGames/flambe