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! 
I went with the creation of the ``Table`` so that an error would be raised if there are duplicate ids after updating. What do you think - worth doing this way for that, or should I just do an explicit check. I'll defer to what you guys want.