Print color diff of actual and expected output to highlight non-printable symbols

[ligurio]

Sometimes test output contains non-printable symbols and it is difficult to understand the difference between actual and expected output when such symbols present in test output.
The solution is implement color diffs that will highlight difference for strings.

Example: Python 3 changed JSON output by default and box-py/call.test.py test output has changed. But it is not clear a difference for both output:

[001] @@ -587,7 +587,7 @@
[001]  ---                   
[001]  {
[001]      "error": {                      
[001] -        "code": "ER_PROC_LUA", 
[001] +        "code": "ER_PROC_LUA",
[001]          "reason": "eval:1: unexpected symbol near '!'"
[001]      }
[001]  }
[001]

@Totktonada advised to use diffc that highlight difference that shows symbols absent in reference output:

To implement a feature we can use diffc or icdiff (https://github.com/jeffkaufman/icdiff).