allow area_options.groupBy to accept either a string or an array for multiple groupings

A map has multiple groups which are defined by separate attributes and each needs its own group case. area_options.groupBy now converts itself to an array if it isn't one already and then uses $.each() to iterate over the attributes to group by when moused over.
Merge pull request #2 from duanemoody/patch-1

allow area_options.groupBy to accept either a string or an array for mul...