add dotfiles support

#492 with whitelist support
taking into account removing the default maybe it would be better to change previous line:
```bash
patterns << "#{dir_name}/#{extra_files}"
```
to
```bash
patterns += [ "#{dir_name}/#{extra_files}" ]
```
?
the `each <<` pattern feels java like (in the monkeys typing form), there are good things in java, this is not one of them.