Change description of stddev and var functions to make it more clear.
Add type signatures to functions so haddock will generate documentation for them
Add export list and section it
Improve function descriptions
Loosen class restrictions from Floating to Fractioanl where possible
More Floating -> Fractional transitions
Add meanWgh function. It calculate mean of sample with weights

This function should be made numerically stable. Even better variant is to
generalize mean and other functions for which weights make sense.
Improve documentation for pearson skewness coeffs.
Improve readability of mean by makeing lambda named function
Merge pull request #1 from Shimuuar/master

Patches for hstats