Pyrsistent

* Fixes 14 where a file executed (unexpectedly) during installation was not python 3 compatible.

v0.7.0, 2015-01-04, No 1.0, instead a bunch of new stuff and one API breaking change to PMap.remove().
* Evolvers for pvector, pmap and pset to allow simple and efficient updates of multiple elements
in the collection. See the documentation for a closer description.
* New method mset on pvector to update multiple values in one operation
* Remove deprecated methods merge and merge_with on PMap
* Change behavior of PMap.remove, it will now raise a KeyError if the element is not present.
New method PMap.discard will instead return the original pmap if the element is not present.
This aligns the PMap with how things are done in the PSet and is closer to the behavior of the
built in counterparts.

* Python 2.6 support, thanks wrmsr!
* PMap.merge/merge_with renamed to update/update_with. merge/merge_with remains but will be
removed for 1.0.
* This is a release candidate for 1.0! Please be aware that PMap.merge/merge_with and immutable()
will be removed for 1.0.

* Fix typo causing the pure python vector to be used even if the C implementation was
available. Thanks zerc for finding it!

* Renamed 'immutable' to 'pclass' for consistency but left immutable for compatibility.

* New data structure, persistent linked list
* New data structure, persistent double ended queue

* New data structure, persistent bag / multiset
* New functions freeze and thaw to recursively convert between python
built in data types and corresponding pyrsistent data types.
* All data structures can now be pickled
* New function merge_in on persistent map which allows a user
supplied function to implement the merge strategy.