Add newick format

Ready for review

I still need to add `read` and `write` as well as deprecate `to_newick` and `from_newick`

@wasade I am particularly interested in any comments you might have.

fixes #627 
Can you use `assertRaisesRegexp` here to ensure that the proper error cases are being hit for each of the files? See the [ordres tests](https://github.com/biocore/scikit-bio/blob/master/skbio/io/tests/test_ordres.py) for an example.