Updated src/sta.cpp.

	- Changed population flag to sample flag. This were due to ambiguity in it's name; it meant return the expected population standard deviation, not that the imput was the population of scores. Using the sample flag and changing variable names so that code now matches definitions used in [Population variance and sample variance](http://en.wikipedia.org/wiki/Variance#Population_variance_and_sample_variance)
	- Fixed bug with compensated sample standard deviation.
Merge branch 'master' of https://github.com/simonccarter/sta

Conflicts:
	src/sta.cpp