def register_column(type, name)
      type = type.to_s.downcase
      raise ArgumentError.new("invalid column type #{type}, permitted types are #{COLUMN_TYPES.join(', ')}") unless COLUMN_TYPES.include?(type)
      @table_columns << name.to_s
      @column_types.merge!(name.to_s => type)
    end
def register_column(type, name)
      type = type.to_s.downcase
      raise ArgumentError.new("invalid column type #{type}, permitted types are #{COLUMN_TYPES.join(', ')}") unless COLUMN_TYPES.include?(type)
      @table_columns << name.to_s
      @column_types.merge!(name.to_s => type)
    end
Registers each column explicitly, with data type, and a name associated
 @param [String] type the type of data column being registered, valid input here are entries from DataTable::COLUMN_TYPES
 @param [String] name the column name that will be used as a label on the graph