Shipping charges not proportional to weight

Hi,

I've had to implement a provider for shipping via La Poste in France recently, and the simple shipping provider isn't usable, because the price is for example, 5 euros up to 500 grams, then 6 euros up to 750 grams, 7 euros up to 1 Kg, etc.

So, I wrote this provider and since I think it could be useful for others and I didn't know if there was another place to post it, here it is.