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! 
it might be easier to make a copy first with:

```python
tcopy = self.copy()
```

and then update the IDs directly?

```python
if axis == 'sample':
    tcopy._sample_ids = updated_ids
else:
    tcopy._observation_ids = updated_ids
```