Tradingstrategy

- Fixes 99 by conditionally importing ib modules

- safediv added to Stochastic from Pull Request 97
- Initial integration fo ib feed/broker. Can operate but it is not yet fully
ocmplete
- Comprehensive ib testing sample
- Added "store" and "data" notifications to cerebro and strategy for the
integration of live feeds
- Internal datetime clarifications
- Fixes 94 removing leftover decode('utf-8') after removing 'b' from 'rb'
when opening csv files
- Fix bug in strategy.close and add plimit support to it
- Some documentation updates

- Memory saving schemes (exactbars parameter to cerebro) full implemented
- Add mixing-timeframes to the docs
- Add memory-savings to the docs
- Cosmetic corrections to data-resampling sample

- Address 84 86 by implemting a LinesCoupler lines object which fills longer
timeframe lines with shorter timeframes
- Add sample for LinesCoupler
- New links for readthedocs io domain
- Detection Improvement for objects supported by writers

- Add 3 new indicators (from 81): PivotPoint, FibonacciPivotPoint,
DemarkPivotPoint
- Add new function CmpEx
- Change plotinit to the intial stages of plotting
- Add plotinfo information to any LineSeries objects
- Implement LineActions Cache
- Implement Indicator Cache
- Cover resampling across midnight border 81
- Correct error in docs (concepts) 82
- Addresses 82 by only advancing indicators in runonce mode if the clock
has overtaken it
- Addresses 82 by having LinesOperations define and internal clock which
may not be the owner

- WeekDaysFiller sample for 76
- Implement new memory saving schemes. Addresses 74
- Additions/Refactoring to the intenal api offered to filters and internal
utils objects and removal of leftover prints
- Refactoring of replay/resample filters
- Some testing refactoring
- Support for cross-plotting across datas of different timeframes
- PivotPoint sample for 81