genltl has bogus short options

Here is an extract of the genltl --help output in 2.3.1:

 Output options:
  -!, --positive             output the positive versions of all formulas (done
                             by default, unless --negative is specified without
                             --positive)
  -", --negative, --negated  output the negated versions of all formulas
  -0, --zero-terminated-output   separate output formulas with \0 instead of \n
                             (for use with xargs -0)

The unwelcome -! and -" short options appeared as a side-effect of #80 (closed), because introducing new LTL families shifted the values of OPT_POSITIVE and OPT_NEGATIVE so they are equal to 21 (!) and 22 (").

We need to start this entire enum at 256, as done in the other tools; however be careful the family options also serve as index in a few tables.