FmeasureAnalysisStrategy implemented. Before it was not working
properly. 

Precision and recall, as well as F-measure, have been studied in the
following materials:

- http://en.wikipedia.org/wiki/Precision_and_recall - F-measure is well
explained.
- http://www-users.cs.umn.edu/~kumar/dmbook/ch8.pdf - Page 64 has a
great example of precision and recall.