ColumnToIndex maps a column to a zero based index (e.g. A = 0, B = 1, AA = 26)
IndexToColumn maps a column number to a coumn name (e.g. 0 = A, 1 = B, 26 = AA)
CellReference is a parsed reference to a cell. Input is of the form 'A1', '$C$2', etc.
ParseCellReference parses a cell reference of the form 'A10' and splits it into column/row segments.
ParseRangeReference splits a range reference of the form "A1:B5" into its components.