def init_mapper(file)
        File.new(file, 'r').each_line do |line|
          from, to = unstring(line).split(':')
          mapper[from] = to
        end
      end
def init_mapper(file)
        File.new(file, 'r').each_line do |line|
          from, to = unstring(line).split(':')
          mapper[from] = to
        end
      end
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