fixed PlainTextResultFormatter to be usable for feature summary generation
+ added SummaryFileWriter allowing to save feature results summary to file in specified format
+ added SummaryGenerator with multiple summary writers support to aggregate and save feature results
+ added support for feature summary format/file name configuration in app.config file.
+ modified FeatureCoordinator to use SummaryGenerator as default Aggregator and use app.config to configure it
+ obsoleted TestResultsSummary and FeatureSummaryAggregator classes
+ modified example project to present how to use feature summary with app.config
+ updated QuickStart.txt and README.md