add Fmeasure
Merge branch 'master' of https://github.com/kuoliu/ActiveLearning into HEAD

Conflicts:
	src/edu/cmu/al/experiment/Evaluator.java
	src/edu/cmu/al/experiment/ExperimentResult.java
	src/edu/cmu/al/experiment/PlotInterface.java
	src/edu/cmu/al/main/Main.java