Add newick format

Not ready for merge
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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 
The existing `from_newick` parser has a long history of dealing with "interesting" trees. Has this reworked method been benched against the old, and shown to parse Greengenes and SILVA trees? If you don't have either, I can provide via email. Same comment re: `to_newick`