Add turf.difference and turf.union

Hello, this port is very nice overall but it would be nice if it could have the difference and union transform operations. We have a product using turfJs and we have a new product that is processing a shape file and converting it to t geoJson. Part of this is calculating the area, we want to match the area calculation algorithm to match our js implementation but the lack of the difference and union operations is preventing us from doing so at the moment.

首先定位 Java SDK 中现有的 Turf 和 GeoJSON 操作入口点，然后将其与 Turf.js 中 difference 和 union 的行为进行比较。使用 shape-file 转 GeoJSON 和面积计算这一用例作为验收上下文；当两个操作都可用，并且针对该工作流产生匹配的结果时，即视为完成。