Added 'filter' command line option

Used to add filters by name. Can be called multiple times, or
with a comma-separated list of filters.
Numeric presets for 'text-lossy' script

Similar to levels in other compressors (e.g. gzip), numerical
preset options '-1', '-2' and '-3' correspond to "typical"
configurations, namely
  1 = lower
  2 = lower + whitespace
  3 = lower + punctuation_sp + whitespace

Also stopped adding a newline at the end, this looked better with
prompts, but made the script no longer idempotent.
Switches 'paragraph' and line-based presets

The 'paragraph' command line switch sets the input to "paragraph
mode" (sets $/ to ''). This means blocks of text are separated
by blank lines, not newline characters.

Most useful with the 'whitespace_nl' filter, or with the new
presets '2l' and '3l', which work like '2' and '3', but with the
'whitespace_nl' filter instead.