new SizeFormatter()
Creates a new style Formatter that returns a proper size value for
any given data value.
The options parameter is a JSON object containing several optional
properties, such as: 
-  scale the scale used to format or classify data values.
 If not specified, the default logarithm scale is used.
-  numClasses the number of classes or buckets to use.
-  startingSize  The minimum or starting size; for any computed size, if it's smaller
 than this value, then use this instead.
-  delta  the delta in size between any two adjacent classes
-  defaultSize  the default size to use when the data value is null
 or a proper color cannot be determined. This color is typically
 used to render shapes with no data. Default is 0 (which means
 the marker will not be displayed).
-  style   the (Marker) style which this formatter is applied to. Optional.
- lengthUnit {String} the unit of the size, value can be "pixel" or "kilometer"; the default unit is pixel
Methods
- 
    resolve(itemValue, column, feature)
- 
    
    The main function of the SizeFormatter. It computes and returns a size 
 value based on the specified data item value and the set of all possible
 data item values (captured as a Column).Parameters:Name Type Description itemValueobject the value of a specific data item, against 
 which the optimal style attribute value (such as fill color or marker size)
 is determined.columnobject the OM.Column instance that contains the set of 
 all possible data items. itemValue is the value of one of the data items
 from the column.featureobject the feature object being resolved. Returns:the determined style size value - Type
- object