[Feature Request] Support XDG_CONFIG_HOME for user data dir.

[kevinhwang91]

static const char* get_ibus_rime_user_data_dir(char *path) {
  const char* home = getenv("HOME");
  strcpy(path, home);
  strcat(path, "/.config/ibus/rime");
  return path;
}

Please support $XDG_CONFIG_HOME.