Adding support to default integer return values

Implementing issue #95, for now adding support only for integers. If i is ok we can move on to other data types.
Sadly this s already done ll over the place on cpputest (at least on the mock support), my vim is configured to only use spaces. There is already an issue open to create a guideline, AFAIK we don't have one right now, there is no definition if it should be spaces or tabs.