ADDED: showterm.el and showterm.pl to draw terms as trees in Emacs

tools/README.md

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+# Showterm: Draw Prolog terms as trees in Emacs
+
+To try it, you need the following programs installed:
+
+- [**Scryer Prolog**](https://github.com/mthom/scryer-prolog)
+- `dot` (from Graphviz)
+- `convert` (from ImageMagick)
+
+Copy [`showterm.el`](showterm.el) and [`showterm.pl`](showterm.pl) to
+the same directory, say `~/scryer-prolog/tools/`, and add to your
+`.emacs`:
+
+    (load "~/scryer-prolog/tools/showterm.el")
+
+If necessary, set `scryer-prolog-path` to the Scryer Prolog
+executable by adding to your `.emacs` (adapting as appropriate):
+
+    (setq scryer-prolog-path "/usr/local/bin/scryer-prolog")
+
+The function `showterm` draws the Prolog term in the region as
+a tree. You can invoke it with `M-x showterm RET`, or for example
+by binding it to a key in your `.emacs`, and then pressing
+that key:
+
+    (global-set-key [f12] 'showterm)
+
+Enjoy!
+
+**Screenshot:**
+
+![Showterm example](showterm.png)