1) Switched + / - and red / green in diffs. It seems like that style
   is more natural to most people.

2) Short primitives do not use the diff anymore. Especially short
   numbers can be read well like 1 !== 2. Cases that can not be
   displayed like that (e.g., -0 and +0) use the regular diff output.

3) Improved error descriptions. It was not always clear what the
   messages stood for. That should now be resolved.

4) Added a position indicator for single lines in case a tty is used
   and the line is shorter than the visual columns.