owt client windows

• 安装编译
• windows 需要openssl 和 boost
• 我觉得脚本会默认用最新的vs工具链吧，我机器就是vs2019 preview
• 我默认的BOOST_ROOT是指向了vs2015版本的boost1.66

Build
Windows
Set environmental variable BOOST_ROOT to your boost source tree.
Run gclient sync.
 It may take a long time to download large amount of data.
Go to src/srcitps/ directory, and run: 

python build-win.py --gn_gen --sdk --tests --ssl_root /path/to/ssl --msdk_root /path/to/msdk --output_path /path/to/out. 

The built binary will be under output_path, the document for sdk will also be copied to this directory if docs has been generated. If not set output_path, the built binary will be under src/out directory. Be noted the first time you run this would take a long time to pull chromium/webrtc dependencies and require a network accessible to Google's code/storage infrastructure.
 ssl_root to the directory of your OpenSSL