Treeswift

* Fixed bug where `Tree.deroot` forgot to set the `Tree.is_rooted` flag to `False`

* Fixed `Tree.deroot` (https://github.com/niemasd/TreeSwift/issues/20); thanks balabanmetin and ekmolloy!

* Refactored code for small performance gains (https://github.com/niemasd/TreeSwift/pull/26); thanks Uzaaft!
* Added support for escaping labels using `'` just like in [`skbio`](http://scikit-bio.org/docs/0.2.2/generated/skbio.io.newick.html#module-skbio.io.newick) (https://github.com/niemasd/TreeSwift/issues/27); thanks valevalorin!
* Also added support for spaces after commas, e.g. `((D, E)B, (F, G)C)A;`

* Fixed bug in `reroot` (https://github.com/niemasd/TreeSwift/issues/24); thanks smirarab!

* Added weighted vs. unweighted option to `Tree.distances_from_root()` and `Tree.height()`
* Used to only support weighted distances

* Fixed bug when writing an output Newick tree that has node/edge params
* Newick writing seems to now work in all of the following scenarios for any node in the tree:
* With/without node labels
* With/without edge lengths
* With/without node params
* With/without edge params