ltlcheck: Add a man page.

* src/bin/man/ltlcheck.x: New file.
* src/bin/man/Makefile.am: Add it.
* src/bin/ltlcheck.cc: Arrange help text.

src/bin/man/ltlcheck.x

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+[NAME] ltlcheck \- translate LTL/PSL formulas into Büchi automata
+[DESCRIPTION]
+.\" Add any additional description here
+[EXAMPLES]
+The following commands compare never claims produced by ltl2tgba(1)
+and spin(1) and 100 random formulas, using a timeout of 2 minutes.  A
+trace of the execution of the two tools, including any potential issue
+detected, is reported on standard error, while statistics gathered
+(normally sent to standard output) are redicted to \f(CWresults.json\fR.
+
+\f(CW% randltl -n100 --tree-size=20..30 a b c | \e
+.br
+ltlcheck -T120 'ltl2tgba -s %f > %N' 'spin -f %s > %N' > results.json\fR
+
+The next command compare lbt, ltl3ba, and ltl2tgba(1) on a set of
+formulas saved in file \f(CWinput.ltl\fR.  Statistis are again
+redirected to \f(CWresults.json\fR.  Note the use of \f(CW%L\fR to
+indicate that the LBT formula should be written into a file, and
+\f(CW%T\fR to read the output in LBTT's format (which is a superset of
+the format output by LBT).
+
+\f(CW% ltlcheck -F input.ltl 'lbt < %L > %T' 'ltl2tgba --lbtt %f > %T'\fR
+
+[SEE ALSO]
+randltl(1), genltl(1), ltlfilt(1), ltl2tgba(1)
+
+[BIBLIOGRAPHY]
+ltlcheck is a Spot-based reimplementation of a tool called LBTT.  LBTT
+was developped by Heikki Tauriainen at the Helsinki University of
+Technology.  The main motivation for the reimplementation was to
+support PSL, and output more statistics about the translation.
+
+The sanity checks performed on the result of each translator (by
+either LBTT or ltlcheck) are described in the following paper.  Our
+implementation will detect and reports problems (like inconsistencies
+between two translations) but unlike LBTT it does not offer an
+interactive mode to investigate such problems.
+
+.TP
+th02
+H. Tauriainen and K. Heljanko: Testing LTL formula translation into
+Büchi automata.  Int. J. on Software Tools for Technology Transfer.
+Volume 4, number 1, October 2002.