Fix Array operations

[eltoder]

• Expose more arithmetic operations. Fix wrapping of division (__div__ method is no longer used in Python 3).

• Make Array * Array return the element-wise product instead of the dot product. This is consistent with QuantLib C++ API and Numpy. Use the matmul operator (@) for the dot product.

• Expose comparison operations (== and !=)

Fixes #661

[lballabio]

Thanks! I must confess I didn't even know matmul existed :)

[eltoder]

Matmul was only added in python 3.5 (PEP 465).

[lballabio]

Yes, only nine years ago :)