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.
Likewise my vim, I always have to :noexpandtabs before editing CppUTest ;P

There should be a guideline, but I think @ryanplusplus is right that tabs are used in most places at the moment :( I've been looking whether github can automatically convert tabs/spaces, but it seems it cannot. Making them the same as the rest of the code (e.g. tabs in this case) would be a good idea.