x64 and Windows support for ndarray

Dear ndarray team,

we are using Boost.NumPy and the ndarray project in a big data context at our lab. So I made the effort and made both projects x64 Python compatible, as well as the ndarrays 64bit indexed (similar to eigen3). I was mainly working on Windows and had to test the projects, so at the same time I extended the SCons build system to work with Windows.

After all changes, both projects build without any internal warnings (the numpy interface deprecation warning left aside) and are working flawlessly on Windows and Linux. All tests are passing.

The changes here are extensive, but focus on x64 indexing for the arrays. The number of dimensions is still left to be an integer, as well as the int fftw-interface is still used (but can now also easily be replaced by the x64 interface).

I am ready to answer questions and hope it is a useful contribution to the project!

Best,
Christoph