Add TODO note
Remove unsupported option
Fix documentation error
Fix issue with multiple columns using same field

Field definitions that boiled down to the same orm starting fragment
were being lost due to storage in a dictionary.  This promises that the
sum of the length of the two returned objects will be equal to the one
object that went in.
Reorder imports
Add utilities to remove redundancy
Implement use of new utilities
Avoid manual building of attr strings
Remove outdated inline documentation
Remove unused keyword argument

This was useful for filter_real_fields, but not really for
split_real_fields, because the latter is only used against the ordering
list.
Add basic tests for utilities
Implement more namedtuples
Add DatatableStructure tests
Adjust DEFAULT_OPTIONS to reflect normalization algorithm
Add docstring
Remove unsupported options from defaults
Add unsortable_columns to options normalization
Remove redundant check
Implement use of new utility
Implement use of new utility