Generates an exponential curve from the start value to the end value. Both the start and end values must be non-zero and have the same sign.
| start | 
 Starting value.  | 
| end | 
 Ending value.  | 
| dur | 
 Duration in seconds.  | 
| mul | 
 Output will be multiplied by this value.  | 
| add | 
 This value will be added to the output.  | 
| doneAction | 
 A doneAction to be evaluated when the line is completed. See Done for more detail.  |