latexmk filter script - unresolved references

Unresolved references should be colored:
```
Latexmk: ====Problematic refs and citations with line #s in .tex file:
  Hyper reference `unittests/index:unittest' on page 5 undefined on input line 121
  Hyper reference `CodeCoverage:codecov' on page 5 undefined on input line 135
  Hyper reference `DocCoverage:doccov' on page 5 undefined on input line 153
```