Brian: Added reset() to mutable stats object and added test for total tweets stat.
Brian: Added reset() to mutable stats object and added test for total tweets stat.
Renamed some fields in CurrentStats for clarity.
Changed TweetInfo to hold values instead of futures, because this was unnecessarily tricky.
Moving performance tests to PerformanceSpec.
Refactoring statistics to be functions.
Added tweets with urls stat.
Brian: Added percentage stats.
Brian: Added photo urls stat.
Added remaining metrics and refactored more stats to functions.
Refactored TweetInfoExtractors to simpler form.
Minor refactorings related to TweetInfoExtractor structure.