Update Makefile

1./etc/config下的配置文件都是uci的配置文件，所以建议将shadowsocks.json置于/etc/shadowsocks.json
2.PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_NAME)-$(PKG_VERSION),为两个版本设置不同的编译目录，否则当同时编译两个版本时出错
3.优化安装脚本
Update shadowsocks.init

1.使用OpenWrt提供的service_start及service_stop函数控制服务开关
2.由service_start函数生成pid文件
3.改配置文件目录为/etc/shadowsocks.json
Merge pull request #50 from nanpuyue/patch-1

refine openwrt build / init scripts
Merge pull request #51 from linusyang/applecc

Support for Apple's CommonCrypto API
darwin: applecc: fix iv not randomized issue