1. boost官网下载，解压，.\bootstrap，.\b2;
2. github下载 clone完，.\bootstrap，.\b2 headers
==》github上为了适应submodule机制 ，所有头文件都分配进了对应的模块里；b2 headers重建boost目录
NOTE: Following Boost modularization and move to Git, header files were moved to their corresponding libraries, into an include subdirectory. For example, the header files of Boost.Filesystem are now in /libs/filesystem/include. For compatibility, /boost sub-directory is now a "virtual" directory, containing links to the headers. The command b2 headers creates or recreates the contents of this /boost directory. https://github.com/boostorg/boost/wiki/Getting-Started