DOC: python-as-glue: remove Instant, PyInline

Both projects appear to be dead.
DOC: remove Weave recommendation

Weave is dead. It's not removed from SciPy yet, but it's deprecated and
doesn't work with Python 3.
Merge pull request #5288 from larsmans/glue-docs

DOC: Python as glue
ENH: add BagObj.__dir__ to numpy.lib.npyio

This allows dir(bagobj), and also enables tab-completion on a BagObj,
which can be useful in an interpreter or IPython