python: Add python bindings for virDomainMemoryStats
Enable virDomainMemoryStats in the python API. dom.memoryStats() will return a
dictionary containing the supported statistics. A dictionary is required
because the meaining of each quantity cannot be inferred from its index in a
list.
* python/generator.py: reenable bindings for this entry point
* python/libvirt-override-api.xml python/libvirt-override.c: the
generator can't handle this new function, add the new binding,
and the XML description