Some values of the Jacobi theta functions were wrong as of version 2.1.0.

Added some unit tests.

New function

`halfPeriods`

, computing the half-periods from the elliptic invariants.New function

`ellipticInvariants`

, computing the elliptic invariants from the half-periods.

The case when the elliptic invariant

`g2`

is zero is now handled.The method computing the half-periods ratio when the elliptic invariants are given led a wrong sign sometimes.

- Minor fix in the C++ code.

Weierstrass sigma function.

Weierstrass zeta function.

Costa surface.

Vectorization.

Better accuracy.

First release.