returns a single value if x is a vector, otherwise a named
vector of size = ncol(x).
Details
This function calculates the skewness of data which is a measure of the
asymmetry of the probability distribution of a real-valued random variable
about its mean. The formula used is:
$$\frac{E[(X-\mu)^{3}]}{(E[(X-\mu)^2])^\frac{3}{2}}$$. This formula is the
typical definition used in many older textbooks and wikipedia