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 
Instead of the `return False, {}` statements, why not just raise `NewickFormatError`? End effect should be the same but the benefit is that the method would be reduced to only two returns.