Backtrader

- Add samples following 'Close' order corrections/improvements for
testing. Addresses 62
- Improve 'Close' execution support and correct conflicting behavior
with method checksubmit. Addresses 62
- Correct method close of strategy by using kwargs which was not
taking into account the existence of a plimit parameter in methods
buy/sell and would pass the execution type as plimit
- PandasData extension sample and data supporting discussion in
ticket 65
- If datas have been passed to cerebro, ensure cerebro has a
strategy to run against (which can get indicators, analyzers,
observers and other through the appropriate interface)
- Addresses 64 by auto-cloning datas in resampledata if the data
was already in the system
- Return a list in case cerebro.run is not run due to missing datas

- Update of bidask sample
- SessionFiller correction to avoid moving the evaluated bar too early into
the stack and avoid the previous session to fill into new session

- Remove old DataReplayer/DataResampler and cerebro resampledata_old and
replaydata_old which were using them
- Adapt docs and test to remove DataReplayer/DataResampler and document the
newer interfaces
- Add ``linesoverride`` parameter to enable redefining the lines of an object
at any stage. Allows removing OHLC default support
- Generalized GenericCSV to use the defined line aliases
- Generalized tick assignment to use the defined line aliases

- Closes 61 by checking datamaster against None to prevent operator
overloading to evaluate the object as False because line 0, contains a value
of 0 at index 0

- Closes 49 by setting the matplotlib backend to "tkagg" to avoid using other
non-tested backends
- io.StringIO instead of internally imported one from py3
- CSVDataBase unicode/bytes unification and also for YahooFinanceData feed
- yahoodownlaod tool bytes/unicode clarification and urlopen bug correction

- Fixes 55 and improves management of CSV subclasses opening a file from
other sources
- Sample which tests yahoo online downloading