docs: def save(self, filename):
          """Save the configuration to a file"""
          filename = pathlib.Path(filename)
          out = []
          keys = sorted(list(self.keys()))
          for key in keys:
              out.append("[{}]".format(key))
              section = self[key]
              ikeys = list(section.keys())
              ikeys.sort()
              for ikey in ikeys:
                  var, val = keyval_typ2str(ikey, section[ikey])
                  out.append("{} = {}".format(var, val))
              out.append("")
  
          with filename.open("w") as f:
              for i in range(len(out)):
                  # win-like line endings
                  out[i] = out[i]+"\n"
              f.writelines(out)