[Cython] array expressions

[mark florisson]

Hey,

Here a pull request for element-wise array expressions for Cython:
https://github.com/cython/cython/pull/144
It includes the IndexNode refactoring branch as well.

This has been the work this last summer for the gsoc, with great
supervision from Dag, who helped steer the project in a great
direction to make it reusable (it's partially included in Numba and
will likely be in Theano in the future, hopefully others as well). I
also wrote a thesis for my master's, which can be found here
https://github.com/markflorisson88/minivect/tree/master/thesis, which
can shed
some light on some parts of the design and performance aspects.
Performance graphs can also be found here:
https://github.com/markflorisson88/minivect/tree/master/bench/graphs

So anyway, how would you prefer dealing with the minivect submodule?
We could include it verbatim, with any modifications made to minivect
directly, since we'd have separate git histories. We could
alternatively make it an optional submodule which is only required
when actually using array expressions. I like the latter, but anything
is fine with me really.

Mark