[issues-21] Replaces hardcoded class/data attribute names with variables

Allows the implementor to define the class names or data attribute names
to use when generating the stylesheet.
[issues-21] Updates examples to show how to redefine the classname.
[issues-21] Updates attribute example with the custom attribute
Merge pull request #28 from leadiv/issues-21

Issues 21 Allow custom naming of the column class