Improvements to wrapping.

Improvements to wrapping.

- Introduce \<space> to indicate line-break positions to enable sensible
  wrapping of Chinese and similar text.
- Allow lines to be longer than the wrapping width if there are no spaces, as
  generated email addresses (e.g. for moderation) won't work if split.
- Fix a bug where using a whole line while wrapping would turn wrapping off as
  the saved (empty) remaining portion would be considered a blank line.
- Use int rather than size_t for line lengths; it's just easier, since we use
  negatives for certain conditions, and it should be plenty big enough.