This is a reworked version of unexpand. I did this for two main
reasons:
1. The previous version of unexpand had issues correctly computing
tabstops when the `-a` flag was supplied.
2. The previous version assumed the input was UTF-8. This version works
with non-UTF-8 inputs.
3. This version has a new flag, -U, which forces unexpand to
treat input as 8-bit ASCII rather than interpreting it
as UTF-8. This might be handy in some cases.
