Add support for 'WithModificationTIme()' option

In some situations I need to set modification time for the new file.

Having an Option `WithPermissions`

```go
func WithModificationTime(time time.Time) Option {
return optionFunc(func(cfg *config) {
cfg.modTime = &time
})
}
```

that takes provided `time` into account and updates the resulting file would make it possible.