自己实现的Spline差值曲线，可以设定起始正切值，默认为0，可根据需要设定为1.同时也支持柱状图显示。并且实现为View，可以在Xib上放置，只需在viewDidLoad时为其指定横坐标显示内容和各个点的横竖坐标值。横坐标显示内容不需要和设定点的数量一致。-Spline interpolite value curve. You can set up its tan value manualy,default is 0,you can set it as 1 if you need. Support Bar chartview too. It is implemented as a view, so you can put it in a xib too. You just set up its x-axis values and the points you want to show. x-axis values amount can be different from points amount.