support specifying build config file by CLI arg

[nighca]

fix #70

• CLI arg BUILD_CONFIG_FILE to specify build config file (superior to $BUILD_ROOT/build-config.json)
• support local file path as value of extends in build config
• pass logger to fork-ts-checker-webpack-plugin

[nighca]

@doxiaodong 搞一波~

[doxiaodong]

README 里面应该加一个可以指定 build-config.json 文件

[nighca]

@doxiaodong 现在 README 里还没有对于 CLI 工具的命令/参数的说明，所以先没加，等后边加了 CLI 工具本身的文档，再说明吧？