code: def init_mapper(file)
          File.new(file, 'r').each_line do |line|
            from, to = unstring(line).split(':')
            mapper[from] = to
          end
        end
docs: Initializes the mappings. A mapping consists of the value to be mapped
   to another value. The values are spearated by colons ':'
   Example:
       source_value:mapping_value