[Cython] Draft for operator overloading

[Dag Sverre Seljebotn]

> about the internals there it was a fuzzy point. Basically, the C++-style
> operators should be in the PXD file as they only are declarations and
> don't contain any code. However the Python-style operators should be in
> .pyx.

...and merged with the declarations in the .pxd filed, like under "Sharing
extension types" here:

http://www.cosc.canterbury.ac.nz/greg.ewing/python/Pyrex/version/Doc/Manual/sharing.html

Dag Sverre