Add mime APIs

[twose]

新增五个mime相关的API

/**
 * @param $suffix[required]
 * @param $mime_type[required]
 * @return mixed
 */
function swoole_mime_type_add(string $suffix, string $mime_type){}

/**
 * @param $suffix[required]
 * @param $mime_type[required]
 * @return mixed
 */
function swoole_mime_type_set(string $suffix, string $mime_type){}

/**
 * @param $suffix[required]
 * @param $mime_type[required]
 * @return mixed
 */
function swoole_mime_type_delete(string $suffix, string $mime_type){}

/**
 * @param $filename[required]
 * @return mixed
 */
function swoole_mime_type_get(string $filename){}

/**
 * @param $filename[required]
 * @return mixed
 */
function swoole_mime_type_exists(string $filename){}