Bugfix: line wrapping; Add: return status of last call

- Fixed: line wrapping was chaos, shifting upward and off-by-one with
  every new character after exceeding terminal width. This is fixed by
  "escaping" the bell character, so BASH doesn't include it in its
  calculation of prompt length (which impacted positioning/wrapping).

- The prompt now shows the return status of the last program/call to
  run; green when 0 (success) or yellow otherwise (error).