func NewFileCache() Cache {
	return &FileCache{}
}
NewFileCache Create new file cache with no config.
the level and expiry need set in method StartAndGC as config string.
package cache
import (
	"bytes"
	"crypto/md5"
	"encoding/gob"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"reflect"
	"strconv"
	"time"
)
type FileCacheItem struct {
	Data       interface{}
	Lastaccess time.Time
	Expired    time.Time
}
var (
	FileCachePath           = "cache"      
	FileCacheFileSuffix     = ".bin"       
	FileCacheDirectoryLevel = 2            
	FileCacheEmbedExpiry    time.Duration  
)
type FileCache struct {
	CachePath      string
	FileSuffix     string
	DirectoryLevel int
	EmbedExpiry    int
}