Allow multiple --id-property.
Allow multiple --id-property.

tsl3su/WorldMap_Choropleth,maxogden/topojson,studiowangfei/topojson,whoinlee/topojson,AlpinHologramm/topojson,btahir/topojson,youprofit/topojson,hcxiong/topojson,ststeiger/topojson,lyhpcha/topojson,ongerit/topojson,koshlan/topojson,mbostock/topojson