Specifies series curve type.
A curve type has effect for Line, LongData, HistoricalLine, Area and Polar series.
It can be one of the following enumerated values:
- CCT_NO_LINE - no line is drawn between data points.
- CCT_LINE - a simple line is drawn between data points
- CCT_SPLINE - Kochanek-Bartels spline connects all data points in a series
- CCT_SPLINE_HERMITE - Hermite spline connects all data points in a series
- CCT_STEP - Step line connects data points
- CCD_REVERSED_STEP - Reversed step line connects data points