doc: add a spot(7) man page

Suggested by Akim Demaille.  Fixes #171.

* bin/man/spot.x, bin/spot.cc: New files.
* bin/man/Makefile.am, bin/Makefile.am: Add them.
* doc/org/tools.org, NEWS: Mention the new page.

bin/man/spot.x

@@ -0,0 +1,28 @@
+[NAME]
+spot \- Command-line tools installed by Spot.
+
+[SYNOPSIS]
+
+Spot is a C++ library for ω-automata and LTL formulas manipulation.
+It also comes with Python bindings and a set of command-line tools
+that are listed below.
+
+[DESCRIPTION]
+.\" Add any additional description here
+
+[SEE ALSO]
+.BR randltl (1)
+.BR genltl (1)
+.BR ltlfilt (1)
+.BR ltlrind (1)
+.BR randaut (1)
+.BR ltl2tgba (1)
+.BR ltl2tgta (1)
+.BR autfilt (1)
+.BR ltlcross (1)
+.BR ltldo (1)
+.BR spot-x (7)
+
+.UR https://spot.lrde.epita.fr/
+The Spot web page.
+.UE