增加新的接口, 减少数据转换

[wsw0108]

通过定义接口, 来兼容其他类Point类型. 参考:

• https://github.com/hgoebl/simplify-java/blob/master/src/main/java/com/goebl/simplify/Point.java
• https://github.com/hgoebl/simplify-java/blob/master/src/main/java/com/goebl/simplify/PointExtractor.java

[wsw0108]

https://github.com/wsw0108/benchmarks/blob/master/src/main/java/org/maptalks/benchmark/proj4/Proj4mBenchmark.java 未见(明显)性能提升

[fuzhenn]

性能虽然没提升，但避免了不少double[]的创建，应能改善GC，感觉值得修改

[wsw0108]

@fuzhenn 虽然避免了double[]的创建, 但交换条件是forward/inverse只能修改传入的Point类对象. 在泛型里, 根据Java规范, 是没法如下的:

public class Klass<T> {
  public T newInstance() {
    return new T; // error
  }
}