Typing

Hum, I tried to do this but how do you know `my_constant`
If you do it in tables.py, we can replace the typing for each values by you notation but it is just a copy/paste everywhere so I tried to do introspection on the typing part of pythran. The problem is that we have ast.node representation of the constant value. To have the correct value, we have to use constant folding. But if we want constant folding, then why not applying it from optimisation and in this case, no constant appears in the typing part of Pythran.

Finally, we can : 
- Use introspection then why not forcing constant folding?
- Copy paste value everywhere.

I think the first solution is better.