Updated qml-box2d submodule
Merge pull request #71 from kenvandine/submodule-update

Updated qml-box2d submodule
Change Behavior 'entity' property to 'target'

Also, change its type to QQuickItem, so we are not restricted to use it
only with the entity type - the script behavior will be used to control
the image layer scroll and other elements in the future.

Signed-off-by: Roger Zanoni <rogerzanoni@gmail.com>
Add behaviors to Layer elements and a ScrollBehavior

The scroll behavior can update ImageLayer and entities inside a Layer
element. This behavior can be extended by adding new implementations and
handling the target type in the ScrollBehavior class.

- Now the element supports horizontal and vertical scroll.
- Now that the scrolling is made by a script, is possible to ship a lot
  of useful scrolling scripts with the engine, such as a script that
  follows an entity or the mouse; Also the user can program custom
  scrolling behaviors.
- Add a vertical scrolling example
- Add a layer scrolling example
Merge pull request #68 from rogerzanoni/layer-refactor

Layer refactor
Ensure the viewport's contentWidth and contentHeight are set properly
Merge pull request #72 from kenvandine/viewport-size

Ensure the viewport's contentWidth and contentHeight are set properly
Don't crash on invalid SpriteAnimation, fixes #75
Merge pull request #76 from kenvandine/issue75

Don't crash on invalid SpriteAnimation, fixes #75
Reorder the targets to fix installation of the plugin.types, fixes issue 73
Merge pull request #78 from kenvandine/issue73

Reorder targets to fix installation of plugin.types, fixes issue
Fixed typo in docstring for Viewport::vScroll
Merge pull request #79 from kenvandine/typo

Fixed typo in docstring for Viewport::vScroll
Adjusting README to show how to avoid issue #80

Special thanks to @ricardodovalle for helping us on it.

Signed-off-by: Rodrigo Oliveira <rodrigo@deadbodyoutline.com>
Merge pull request #81 from rodrigogolive/macos_build

Adjusting README to show how to avoid issue #80