Added new features to allow multiple data series

## Update in 0.9.2

 * Now supports a different way of passing the inputs
 * Supports more than one data series per chart   
   In the case of bar chart, the values will be stacked according to data sequence. 
 * Supports the selection of marker characters
   User can specify one marker, in which case all line sequences will use that marker. Or user can specify marker at least the same number as the number of data series. 
 * Now allows nil in the y-values, in which case the corresponding point will be left blank