Dual curves

[enriqu...@gmail.com]

I have been gladly suprised lately by the fact that one can compute the dual of a curve in a projective space. It works quite well for me.

I have tried with a curve defined over a number field without success, because the method checks if the ground field is either finite or rational. The algorithm should work on any field (at least on number fields), I do not see what is specific to that case; of course, it may be slower. I defined a function with the code of the method, taking out the restriction on the fields and it seems to work.

I wonder if some restrictions on the fields should be added and if it is worth a PR (I may do it). Best, Enrique.