added tab analysis info to WordInfo

we will handle tabs correctly, by computing the tabstops *while*
linebreaking rather than before like other versions of fmt.
(If the other behavior is desired, just expand before applying fmt)
proper tab handling

We expand tabs correctly now, computing the length of a word about to be
output based on its position on the line. This is in contrast to other
versions of fmt, which expand prior to line breaking; in some cases,
their method will give different (and probably worse) results than ours.