The retinaScale helper now enforces the display size to the correct values because if no style has been set on the canvas, the render size is used as display size, making the chart bigger (or smaller) when deviceAspectRatio is different of 1.
In many cases, the canvas render size is changed by the lib, causing the state stack to be discarded, meaning that we can't use save() and restore() to release the context with its initial state (i.e. before creating the chart). Since we don't need (want) to manually save / restore the context initial state, simply make sure to reset it to the default state to give a fresh context back to the user. That also means we don't need to revert the scale when the pixel device ratio is not 1.
When the iframe is attached to the DOM, its content is reloaded (invaliding the resize listener) so make sure to install the handler after the iframe is loaded. Optimize resize events by throttling resize process until the next animation frame. Rewrite the unit test "waitForResize" method, the previous one (timeout) was too weak and most tests was failing on FF.
Add support for creating a chart from the canvas id and prevent exceptions, at construction time, when the given item doesn't provide a valid CanvasRenderingContext2D or when the getContext API is not accessible (e.g. undefined by add-ons to prevent fingerprinting). New jasmine matcher to verify chart validity.
Responsiveness is currently based on the use of an iframe, however this method causes performance issues and could be troublesome when used with ad blockers. So make sure that the user is still able to create a chart without iframe when responsive is false.
