add unit test, use md5 and psnr to test the validity of decode.

usage:
./unit_test.sh  /root/Videos/h264/Base_Ext_Main_profile/
./unit_test.sh  /root/Videos/vp8/vp8/
./unit_test.sh  /root/Videos/jpg/workdir.jpeg_dec/ /root/Videos/jpg/yuv/
'pwd' is not good, we need change to unit_test directory to run unit test. It's better if we can use script's location as CURRENT_PATH.