func ReadFile(fs FileSystem, path string) ([]byte, error) {
	rc, err := fs.Open(path)
	if err != nil {
		return nil, err
	}
	defer rc.Close()
	return ioutil.ReadAll(rc)
}
ReadFile reads the file named by path from fs and returns the contents.
package docview
import (
	"fmt"
	"io"
	"io/ioutil"
	"os"
)
type FileSystem interface {
	Open(path string) (io.ReadCloser, error)
	Lstat(path string) (os.FileInfo, error)
	Stat(path string) (os.FileInfo, error)
	ReadDir(path string) ([]os.FileInfo, error)
}