use consistent names in documentation

[dr0]

(the following refers to the https://datagraft.net/documentation/#transform_pipeline)
Take/Drop Columns > && Derive Column > && Take/Drop Rows == designated as ‘function’
Map Columns > && Filter Rows == designated as method
Rename Columns > && Split Column > == designated as operation
given the possibility for Clojure expressions to be entered as values for columns I think that a consistency in how the above sidebar function (i.e. predefined transformations) are designated would be helpful. See for instance the use of function in Derive Column : Tips and Tricks and Rename Column: Tips & Tricks