This commit removes the ability to reference a shared TradingEnvironment through the zipline.finance.trading module. In place, the classes that require a TradingEnvironment, or its child AssetFinder, contain their own references to those objects.
This commit also adds serialization utilities that allow for the pickling/unpickling of objects without unintentionally their TradingEnvironments or AssetFinders.
The correct thing to look at to figure out where the root of the
zipline tree is, is `zipline.__file__`, not `zipline.__path__`. The
latter could contain multiple directories in it, and is not intended
to be `os.path.join()`ed as the previous code was doing.
and added a new test case
was not iterating over lookup date directory names, and
therefore mising all by one list of stocks.
discovered because of differing sort orders between
my local machine, other devs, and travis ci.
jfkirk