Paper: Validated numerics in Python with ValidiP (David Sanders)

This is David Sanders's contribution to the SciPy 2014 proceedings: Validated numerics in Python with `ValidiPy`

Now ready for review.
Perhaps this would be clearer if you used `f(x) := x * x` rather than `x^2`.  I suspect that `x^2` works just fine (if you have defined a suitable `pow` operation.  The real issue here seems to be with `*`.