Memory efficient tuple storage

[psaffrey at googlemail.com]

In the end, I used a cStringIO object to store the chromosomes -
because there are only 23, I can use one character for each chromosome
and represent the whole lot with a giant string and a dictionary to
say what each character means. Then I used numpy arrays for the data
and coordinates. This squeezed each file into under 100MB.

Thanks again for the help!

Peter