Integer valued features

The features ln and col for column and line numbers are now integer valued.
The numbers do not contain primes.
If primes are present, it is indicated in the features primeln and primecol.

But I had to do something about comment lines, which got numbers like $a and $b.
These numbers now go into a separate feature lnc (character line numbers or comment line numbers).

Note that the full number, lnno incorporates the column number and the primes and the comment numbers.
This is used for section headings for lines.