Data standardization: z-score and 0-1 scaling

Interface and implementation of data standardization (normalization) techniques. A proposed interface would allow scale data and reverse it to its original state. Currently available: z-score and 0-1 forward scaling.
These are commonly used scaling techniques in data analysis and machine learning.

The idea originated in MLBase package, but it was [proposed](https://github.com/JuliaStats/MLBase.jl/pull/9) to move the code into StatsBase. So my question is whether this functionality should be integrated in StatsBase or move it into separate package.
For cache efficiency, it is desirable to scan column by column, instead of row by row.