tex-showlabels{,-doc}: update to 1.9.1

* Robustness fix: macros in arguments are now handled, so that (after
  \showlabel{index}), \index{Poincar\'e} doesn't cause an error.
* The \showlabel[optarg]{command} optional argument can now take a
  one-argument command.
* The macro \showlabeltype expands to the current label type, for possible
  use in \showlabelsetlabel.
* The code has moved from Bitbucket to Sourcehut: the new repository is
  https://hg.sr.ht/~nxg/showlabels.

(markd)