Add xfaceLib doc and demo
基本实现ios平台库模式打包

主要思路是通过脚本修改开发工程的target，并去掉一些不需要的资源，
然后使用xcodebuild生成.a文件，并与其它资源打包成最终的sdk
解决ios平台编译库时路径拼接不对的问题
1. package demo and doc to xFaceLib.zip when building with lib mode 2. update lib and res and app of demo to lateset when building with lib mode
Merge branch 'dev' of gitlab.polyvi.com:xface/xface-extra-lib into dev
1. using asset tag instead of source-file tag to copy dir 2. rename xFaceLib to xfaceSdk to keep the same with ios