MAINT: Remove redundant perf_tracker member.

The perf_tracker member of TradingMember was set to None twice
during __init__.

Remove one of those instances.
ENH: Change open and close to midnight if using daily input data.
MAINT: Factor out column conversion in HistoryContainer.

We can't be sure that security identifiers can be converted
to int. In fact, most of the times they are strings. This
adds an identity function that can be overwritten if such
a conversion is necessary (as on Quantopian).
TST: Add unittest for daily history with midnight dt.
Merge branch 'history_support_daily_input'
DOC: Add tutorial and update examples to use history.
MAINT: Refactor AlgorithmSimulator.transform.

Breaks out the main snapshot processing loop into its own function, and does
some minor variable renaming-shuffling.

Adds `TradingAlgorithm.on_dt_changed`, a function to be called when the
simulation dt changes, prior to processing any events.

There should be no difference in behavior as a result of this change.
MAINT: Add comments and rename methods in PerformanceTracker.

The function that handles a market close for daily frequency changed from
`handle_market_close` to `handle_market_close_daily`.

The function that is called at on the closing minute each day when running
minutely changed from `handle_intraday_close` to
`handle_intraday_market_close`.
ENH: Remove dividends from the event stream.

Removes support for handling dividends as part of the algorithm
simulation stream, replacing it with an API in `TradingAlgorithm` for
supplying dividends as a DataFrame.
STY: In test_perf_tracking, import datetime/timedelta via from-import.
DOC: Rename 'guid' to 'id' in dividend tracking logic.