[BACK_INCOMPAT] JSON and Cufon are no longer included in default build
[BACK_INCOMPAT] Change default objects' originX/originY to left/top
[BACK_INCOMPAT] fabric.StaticCanvas#backgroundImage and fabric.StaticCanvas#overlayImage are fabric.Image instances. fabric.StaticCanvas#backgroundImageOpacity, fabric.StaticCanvas#backgroundImageStretch, fabric.StaticCanvas#overlayImageLeft and fabric.StaticCanvas#overlayImageTop were removed.
[BACK_INCOMPAT] fabric.Text#backgroundColor is now fabric.Object#backgroundColor
[BACK_INCOMPAT] Remove fabric.Object#toGrayscale and fabric.Object#overlayFill since they're too specific
[BACK_INCOMPAT] Remove fabric.StaticCanvas.toGrayscale since we already have that logic in fabric.Image.filters.Grayscale.
[BACK_INCOMPAT] Split centerTransform into the properties centeredScaling and centeredRotation. Object rotation now happens around originX/originY point UNLESS centeredRotation=true. Object scaling now happens non-centered UNLESS centeredScaling=true.