* src/bin/ltlgrind.cc: New file, command-line tool to get mutations of a
formula.
* src/bin/Makefile.am: Add it.
* src/ltlvisit/mutation.hh, src/ltlvisit/mutation.cc:
New files providing the get_mutations function.
* src/ltlvisit/Makefile.am: Add it.
* src/ltltest/ltlgrind.test: Test it.
* src/ltltest/Makefile.am: Add it.
* src/bin/man/ltlgrind.x: Document it.
* src/bin/man/Makefile.am: Add it.
* doc/org/ltlgrind.org: Document it.
* doc/org/tools.org: Add link to ltlgrind documentation page.
