Update link to PyGeode online documentation.
Workaround a bug in recent versions of numpy (>=1.7).

If a record array has a column of type 'O' (object), then it's not possible
to filter out a subset of columns with the slice notation.

Instead, do it the hard way - pull out each column, zip the data together, then
put it back into a record array (explicitly telling numpy what data types to
use in the subset).

Works around numpy issue 3256 (http://github.com/numpy/numpy/issues/3256)