Support for coveralls.io

[SergeStinckwich]

Add support for tests coverage in the CI with : http://coveralls.io

[SergeStinckwich]

Add support here: https://travis-ci.org/PolyMathOrg/PolyMath but all build fails when I modify .smalltalk-ston to use coverage: https://travis-ci.org/PolyMathOrg/PolyMath/builds/527648159

[hemalvarambhia]

I'll look to break this task up on a package by package basis as it's become quite big now.