名称： site_config
功能： 读取站点设定列表
代码示例：
<title>{$site_config['site_title']}</title>
<meta content="{$site_config['site_description']}" name="description">
<meta content="{$site_config['site_keywords']}" name="keywords">
<meta property="og:site_name" content="{$site_config['site_name']}">
<meta property="og:title" content="{$site_config['site_title']}">
<meta property="og:description" content="{$site_config['site_description']}"> 数据格式示例：
Array
(
[site_name] => 智网企业在线商城
[site_title] => 在线服装商城【模板演示】
[site_keywords] => 在线商城,B2C商城,外贸商城,服装商城
[site_description] => 在线服装商城【模板演示】，是基于智网企业网站管理系统编写，为企业提供快速安全的建站流程
[site_address] => 深圳市罗湖区
[icp] =>
[tel] => 0755-8888888
[fax] => 0788-8888888
[qq] => 169378
[email] => 973432@qq.com
[thumb_width] => 135
[thumb_height] => 135
[mail_host] => smtp.qq.com
[mail_port] => 25
[mail_ssl] => 0
[mail_username] =>
[mail_password] =>
[mobile_name] => 智网企业建站系统
[mobile_title] => 智网企业建站系统
[mobile_keywords] => 智网企业建站系统
[site_theme] => template_1
[mobile_theme] => template_1
[mail_cloud] => 0
[mail_rss_url] =>
[db_cache_time] => 200
[tpl_cache_time] => 86400
[img_captcha] => 1
[weight_unit] => Kg
[unit_freight] => 3
[basic_freight] => 8
[free_freight] => 1000
[clientId] => ...
[clientSecret] => ...
)