Handles the case where pandoc isn't available during download.

Also bumps version up to 0.5.6 so the new version will apply.
Updates README example code to use window_length instead of days.

In a previous patch, the transform argument had been changed
from days to window_length.

The README example was thus not able to be run, updating algo
so that it runs against current versions of transforms.
ENH: Add granularity and annualizer arguments to TradingAlgorithm. Accompanying doc string and unittest.
MIN: Replaced annualizer with a dictionary. Added set_granularity method.
Changes tests from using an ndict for trades to an Event object.

When run over large amounts of data the use of ndict's gets and sets
become a large bottleneck, around 1/5th of the CPU time is spent
in ndict's __setattr__, __getattr__, etc.

By switching to an object for an event,
we reduce the penalty significantly.

Removes asserts that check for event being an ndict, as well as those
that assume a certain behavior of the __contains__ method for events.
Merge pull request #48 from quantopian/change-trade-from-ndict-to-object-based-event

Changes tests from using an ndict for trades to an Event object.
Optimizes checking ready state of sources during sorting.

The main bottle neck here was using `len`.
A boolean check is a sufficient test for more items in the queue.

Also, uses all instead of several functions.
Adds a __repr__ method for Event.
Removes assert of message confirming to protocol.

Two reasons for removal:
- On the path of removing most non-postconditional asserts.
  Since the asserts on every message is incurring a
  non-insignificant penalty on large datasets.
- Since the assert was invoked as a function, the 'right side'
  of the assert statement, i.e. the error message was being invoked
  as a function, discovered since the __repr__ of the message was
  high on the bottleneck list.
Removes assert of sort protocol in inner loop.

Since this was invoked as an function, the invocation of the method
was not dropped by -O.
Also, moving towards only having postconditional asserts.
Updates to latest version of flake8. 1.6.2 -> 1.7.0
MIN: Override annualizer if set. New handling of granularity (no default arg anymore). Renamed minutely to minute.
Removes coverage being run on each internal build of the project.

coverage provides valuable info, but changing to run it less
frequently than every checkin.
Updates msgpack-python to latest. 0.2.3 -> 0.2.4
Upgrades requests to latest. 1.0.3 -> 1.0.4
Adds reprs for PerformanceTracker and TradingEnvironment.

For debugging in the REPL.
Removes random test invocation.
Reduces the the dataset size for performance tracker test.

So that the test is easier to debug and walk through on paper.

Also, removes randomly created dataset.
Enables performance messages on days that have no trades.

Previously, on days that were trading days, but there with no
event data to process for that day, performance metrics were
not emitted, since the handling was based on having an event
trigger the daily performance metric.

Handled by grouping together performance messages, on market open,
for all days since the last market close.

Also, changes perf_tracker unit test to simulate missing data.

Taken from @richafrank's branch handling the same case.
Remove nosexcover from dev requirements for zipline