Add Unitify transform to add units to columns

[juliohm]

It would be nice to be able to save units in column names according to a given standard, and provide transforms to "unitfy" the columns for the user. For example, we could follow the convention that T [K] the variable T has units K. We could then introduce a transform Unitfy that removes the suffix [K] and adds the corresponding unit with Unitful.jl to the array of values.