0.8.1

• yaaay, added some basic unit tests
• skipped the first and the last grid lines from drawing, #174.
• prevent to draw touchedSpotDot if show is false, #180.
• improved paint order, more details in #175.
• added possibility to set double.nan in centerSpaceRadius for the PieChart to let it to be calculated according to the view size, fixed #179.