docs: def to_file(self, filename=None, write_style=True):
          """
          >>> p = Preso()
          >>> z = p.to_file('/tmp/foo.odp')
          >>> sorted(z.ls('/'))
          ['META-INF/manifest.xml', 'content.xml', 'meta.xml', 'mimetype', 'settings.xml', 'styles.xml']
          """
          out = zipwrap.Zippier(filename, "w")
          out.write("mimetype", self.mime_type)
          for p in self._pictures:
              out.write("Pictures/%s" % p.internal_name, p.get_data())
          out.write("content.xml", self.to_xml())
          if write_style:
              out.write("styles.xml", self.styles_xml())
          out.write("meta.xml", self.meta_xml())
          out.write("settings.xml", self.settings_xml())
          out.write("META-INF/manifest.xml", self.manifest_xml(out))
          return out