New ellL1 implementation by Pascal Molin

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

Dear PARI developers,

I have merged Pascal Molin code for computing ellL1 and ellanalyticrank.
The new code is much faster than the old one for derivatives.
For the value of L itself, it is slightly slower, but only because the
older code used unproven (and sometimes wrong) bounds for the summation.

This makes ellheegner faster when the height of the point is large.

Pascal code also includes facilities for computing values of L function and
derivative on the critical line, not just at 1. However this is not
exposed in GP. If you need this feature, we can provide a GP interface to it.

Cheers,
Bill.