文件多线程下载，支持断点续传，非常好的例子-mutiple file download，support stop-point download，good example

文件的分割与合并，亮点在于用了多线程和.net的GC机制，using新用法，想学习的可以下载下来看一下-File split and merge, the highlight of a multi-threaded. NET GC mechanism, using the new usage, want to learn can be downloaded look...