the Column namespace

[bruceravel]

This is one of a short string of issues I am opening up after doing some work on the specification document leading up to #28.

• Is a file non-compliant if the Column fileds are missing?
• Is it non-compliant if the number of Column fields is different from the number of columns?
• Is it non-compliant if the Column field values are different from the words in the column label line at the end of the header?