0.30.0

• [IMPROVEMENT] We now use RenderObject as our default drawing system. It brings a lot of stability. Such as size handling, hitTest handling (touches), and It makes us possible to paint Widgets inside our chart (It might fix #383, #556, #582, #584, #591).
• [IMPROVEMENT] Added Radar Chart Documentations
• [IMPROVEMENT] Added textAlign property in the BarTooltipItem, LineTooltipItem, and ScatterTooltipItem, default is TextAlign.center.
• [IMPROVEMENT] Added direction property in the BarTouchTooltipData, and LineTouchTooltipData to specify the position of the tooltip (can be auto, top, bottom), default is auto.
• [IMPROVEMENT] Updated touch flow, we now use hitTest for handling touch and interactions.
• [IMPROVEMENT] Added 'clickHappened' property in all of our TouchResponses (such as LineTouchResponse, BarTouchResponse, ...), #210.
• [IMPROVEMENT] Added swapAnimationCurve property to all chart widgets which handles the built-in animation Curve, #436.
• [BREAKING] Some properties in ScatterTouchResponse, and PieTouchResponse moved to a wrapper class, you need to access them through that wrapper class.
• [BREAKING] Renamed tooltipBottomMargin to tooltipMargin property in the BarTouchTooltipData, and LineTouchTooltipData
• [Bugfix] Fixed double.infinity in PieChartData .centerSpaceRadius, #584.