add a function to replace unknown words in target sent
add a function to replace unknown words in target sent

add a function to replace the unknown words in target sentences with their aligned words in source sentences.
yang1fan2/nematus,yang1fan2/nematus,shuoyangd/nematus,EdinburghNLP/nematus,rsennrich/nematus,shuoyangd/nematus,Proyag/nematus,rsennrich/nematus,Proyag/nematus,cshanbo/nematus,shuoyangd/nematus,Proyag/nematus,yang1fan2/nematus,yang1fan2/nematus,Proyag/nematus,rsennrich/nematus,Proyag/nematus,cshanbo/nematus,yang1fan2/nematus,yang1fan2/nematus,EdinburghNLP/nematus,EdinburghNLP/nematus,cshanbo/nematus,EdinburghNLP/nematus,shuoyangd/nematus,cshanbo/nematus,EdinburghNLP/nematus,yang1fan2/nematus,rsennrich/nematus,rsennrich/nematus,shuoyangd/nematus,Proyag/nematus,cshanbo/nematus,shuoyangd/nematus,yang1fan2/nematus,yang1fan2/nematus,cshanbo/nematus,rsennrich/nematus,yang1fan2/nematus,EdinburghNLP/nematus