Interpolate parametrized scenarios

[soywod]

The $ in Stages method allows you to get variable tests output. It could be nice if we can have the same thing in parametrized Scenarios. For now we have in the console output :

Should be a parametrized test # 1
Should be a parametrized test # 2
Should be a parametrized test # 3
...

Using $ in Scenarios method, we could get :

Should be a parametrized test toto
Should be a parametrized test tata
Should be a parametrized test titi
...

[flegall]

Implementation of this will rely on #154 fix