Introduction
Composer is a tool for dependency management in PHP. It allows you to declare the dependent libraries your project needs and it will install them in your project for you
全局安装
curl -sS https://getcomposer.org/installer | php
mv composer.phar /usr/local/bin/composer
https://getcomposer.org/doc/00-intro.md#installation-linux-unix-osx
http://docs.phpcomposer.com/00-intro.html#Installation-*nix
