New features and bug fix

• Enable to get element without bindto #208
• Fix to remove class 'c3' when destroy() called #233
• Fix error when mouse over with data.names #197
• Fix line with null on sub chart #229
• Fix tooltip position on the edge - #234
• Fix event rect for timeseries - #225
• Fix check type for pie/donut - #227
• Fix data label position on arc when the chart is small
• Fix y padding when formatted #231
• Fix event rect when width < 1
• Fix update of legend when svg hidden #241