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 add a deprecation warning block to the docstrings for `from_newick`, `to_newick`, and `from_file`? This is recommended by numpydoc, see [this example](https://github.com/biocore/scikit-bio/blob/master/skbio/stats/distance/_base.py#L162).