PERF: Remove deepcopy from EventWindow ticks.

The deepcopy of events into the EventWindow's ticks was causing
a significant increase in memory consumption, e.g. an algorithm with
almost 200 sids and 14 vwaps removing the deepcopy reduces the amount
of memory consumed by about 40%.

The downside is that if an event's properties are changed, which is
not advised, later on, then the signal derived from vwap etc.
may be changed.
ENH: Safe risk_report in TradingAlgorthm.
ENH: Add print of monthly Sharpe to DMA example.
BUG: cum_perfs defined but not used.
ENH: Plot benchmark returns in DMA example.
STY: Flake8 line break.
BUG: Prevent unintended keys from appearing in data bar.

The defaultdict behavior was allowing both algo code and
TradingAlgorithm wrappers to add unintended keys.

Remove use of defaultdict in favor of a dictionary that explicitly
adds the values in tradesimulation, otherwise allow a KeyError
if the bar is indexed with a sid that doesn't exist.

Also, when iterating over the keys in the data bar, only return
those keys that have pricing data.
BLD: Update nose-paremeterized to latest release. (1.3.0)
BLD: Update extra requirements to latest versions.

scikits.learn was renamed to scikit-learn
BLD: Rename extra requirements to goodies.

Since these modules are not requirements, make the name more clear
about the distinction. Especiall, so that build scripts do not pick
up this file when including wildcards whit a requirements prefix.
BUG: Prevent crashes for TALib functions when stocks have nans.

If a stock stops gettign updated values, e.g. if a stock rolls out
of a universe strategy, currently the underlying batch transform
for TALib may have nans (which is another issue that could be addressed),
the nans cause crashes when passed to some TALib function, e.g. Bollinger
Bands are incompatible with all nan values.

So, drop sids that only have nan values for the current data panel.
MAINT: Update Dev requirements

Upgrade matplotlib in Dev requirements to 1.3.0, and add tornado==3.1
and pyparsing==2.0.1 which are required by matplotlib.
BUG: Trading calendar dates should always be midnight UTC

For consistency, datetimes returned by the trading calendar should
always show HHMMSS of midnight UTC. Not only is this useful for
consistency, but it also allows us to check if a particular date() is
in an array of these datetimes, because they will hash to the same
thing. For example:

early_closes = get_early_closes()
... later ...
if current_bar_datetime.date() in early_closes:
    ... today closes early ...

If if the datetimes returned by the trading calendar functions don't
have 00:00:00 for HHMMSS, then the "in" check above will fail because
the date and the datetimes in early_closes won't hash to the same
thing.
MAINT: Move risk to its own module.

In anticipation of splitting apart the different risk classes
into their own submodules, a distinct risk module should help
organize those new classes.
MAINT: Split apart risk metrics classes.

Also remove test that compares risk metrics batch to iterative,
since the 'iterative' calculations, replaced by the cumulative
calculations, will intentionally drift from the results in the risk
report due to annualization and other factors.

Work towards having separate calculations for the fixed periods versus
the cumulative/headline risk metrics.
Different sumbodules for each type should help make the calculations
type distinct and easier to find.
MAINT: Break period and cumulative risk metrics into submodules.

In anticipation of changing the sharpe, beta, et al. calculations
dependent on whether the period returns or the overall returns
are being calculated.
MAINT: Create separate page in risk answer key for period returns.

Copy the `Sim` sheet to `Sim Cumulative` as well as rename it to
`Sim Period`.

Update the answer key module accordingly.
DOC: Fix talib sphinx warnings. Closes #171.
DOC: Updated example in readme and added python-dateutils dependency. Closes #139.
BLD: Add version to zipline, bump to 0.5.11.dev

zipline.__version__ is now present. Closes #94.

Moreover, git master should have a .dev version string according
to convention. Releases then get the .dev label removed.