Fixed wrong Log class reference
Renamed Strategy to Mapper and gave more detailed names: ColumnIndexMapper / ColumnNameMapper
Greatly simplied the mapper implementations
Implemented routine for checking whether indexes or column names in headers exist in a CSV file.
Set Logger classes right for mappers
Cleaned up some more code in the mappers, also exposed Header method to report on the line
Added check for number of columns. Once set, all rows must have the same number of columns.