What about ignoring extra columns if less specified at construction?

[ardabro]

Sometimes I don't want to decode all columns, some csv files have separator after last column.
This forces user to specify, parse and assign unnecessary data.
What about allowing to skip them?
Moreover: What about specifying column range when constructing instance?
io::CSVReader<3,7,... // read columns from 3 to 7 (inclusive or exclusive)