New GP function hyperellratpoints

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

Hello PARI developers,

I have ported Michael Stoll ratpoints code to PARI and added two GP
functions: ellratpoints and hyperellratpoints

ellratpoints(E,h) returns the affine rational points of height
less than h:

? E=ellinit([1,2,3,4,5]);
? ellratpoints(E,1000)
%7 = [[1,2],[1,-6],[-103/64,-233/512],[-103/64,-479/512]]

hyperellratpoints does the same for hyperelliptic curves:

? hyperellratpoints([-x^2-x,x^3+x+1],10000)
%8 = [[-1,1],[-1,0],[0,0],[0,-1],[1,-1],[1,-2],[-12/5,15],[-12/5,28/125]]

I like to thank Michael for writing ratpoints and for encouraging me to port
it to PARI/GP.

Cheers,
Bill.