added Table.update_ids method

@wasade or @ElDeveloper, can one of you review this one? I haven't contributed to biom in a while - let me know if I'm doing anything wrong. The codebase is looking really nice, btw! 
```python
updated_ids = zeros(self.ids(axis=axis).size, dtype=object)
for idx, old_id in enumerate(self.ids(axis=axis)):
   ...
```