CommaSeparatedValuesField now introduces two new methods to the parent

model owning the field:

get_<fieldname>_list()
get_<fieldname>_display()

These both return a version of the stored list using any display names

provided by the choices= passed to the field.
This field was largely written in order to replace

django-multiselectfield, which provided these methods. We lacked

these until now.
The module was also missing from the codebase docs. It's now added.

Unit tests pass.