* src/bin/ltlcross.cc: Implement it.
* src/bin/man/ltlcross.x, doc/org/ltlcross.org, NEWS: Document it.
* src/tgbatest/ltl2dstar.test, src/tgbatest/ltlcross3.test: Test it.
* src/bin/ltlcross.cc: Report exit_status and exit_code columns in CSV
and JSON files. Also output lines for failed translations, and add
a --omit-missing option to disable that. Move the time column right
after exit_status and exit_code.
* src/bin/man/ltlcross.x: Document each column of the output.
* bench/ltl2tgba/tools: Use the "{name}cmd" notation.
* bench/ltl2tgba/sum.py: Adjust to the new columns.
* bench/ltl2tgba/README: Update to point to the man page for a
description of the columns.
* bench/ltl2tgba/Makefile.am: Build results.pdf as said announced in
README.
* bench/spin13/html.bottom: Update code to ignore these two new
columns and lines with null values.
* src/tgbatest/ltlcross3.test: Add tests.
* doc/org/ltlcross.org: Adjust examples.
* NEWS: Mention this.
