Pyrsistent

* Fix 34, PVector now compares against built in list type

* Rename pclass back to immutable and deprecate the usage of the pclass function. PClass will be used by
a new, different type in upcoming releases.
* Documentation strings for the exceptions introduced in 0.9.2.

* More informative type errors from checked types, issue 30
* Support multiple optional types, issue 28

* Multi level serialization for checked types

* Checked types, checked versions of PVector, PMap, PSet that support type and invariant specification.
Currently lacking proper documentation but I'm working on it.
* set_in() on PVector and PMap are now deprecated and will be removed in the next release.
Use transform() instead. set_in() has been updated to use transform() for this release
this means that some corner error cases behave slightly different than before.
* Refactoring of the PVector to unify the type. Should not have any user impact as long as
only the public interface of pyrsistent has been used. PVector is now an abstract base class
with which the different implementations are registered.
* Evolvers have been updated to return themselves for evolving operations to allow function chaining.
* Richer exception messages for KeyErrors and IndexErrors specifying the key/index that caused the failure.
Thanks radix for this.
* Missing attribute on PMaps when accessing with dot-notation now raises an AttributeError instead of a
KeyError. Issue 21.
* New function decorator mutant that freezes all input arguments to a function and the return value.
* Add __version__ to pyrsistent.py. Issue 23.
* Fix pickling for pset. Issue 24.

* New type PRecord. Subtype of PMap that allows explicit, declarative field specification. Thanks boxed
for inspiration!
* Efficient transformations of arbitrary complexity on PMap and PVector. Thanks boxed for inspiration!
* Breaking change to the evolver interface. What used to be .pvector(), .pmap() and .pset()
on the different evolvers has now been unified so that all evolvers have one method .persistent()
to produce the persistent counterpart. Sorry for any inconvenience.
* Removed the tests directory from the package.
* PMap and PSet now contains a copy-function to closer mimic the interface of the dict and set. These
functions will simply return a reference to self.
* Removed deprecated alias 'immutable' from pclass.