Pyrsistent

* Full Python 3 support.
* Immutable object implemented.
* Bug fixes in PVector.__repr__() and PMap.__hash__() and index check of PVector.
* Repr changed to be fully cut and paste compatible
* Changed assoc() -> set(), assoc_in() -> set_in(), massoc() -> mset().
Sorry for the API breaking change but I think those names are more pythonic.
* Improved documentation.

* assoc() on PSet renamed back to add()

* Full Sequence protocol support for PVector
* Full Mapping protocol support for PMap
* Full Set protocol support for PSet
* assoc_in() support for both PMap and PVector
* merge() support for PMap
* Performance improvements to the PVector C extension speed up allocation

* Supply the tests with the distribution

* New C extension with an optimized version of the persistent vector
* Updated API slightly

* Initial release.


TODO (in no particular order)
-----------------------------
- Versioned data structure where the different versions can be accessed by index?
- Ordered sets and maps
- A good performance measurement suite