Increase test coverage to approx. 80%
Increase test coverage to approx. 80%

Changes:
- Remove "parallel" execution of tests because there was no speed gain observable
- Update test for fact to check memoization
- Add tests for `arithmeticMean`, `intersection`, `nGram`, `skipBigram`, `treebankTokenize`, and `fMeasure`

kenlimmj/rouge