modified HPSNR

new version HPSNR for adaptive filter size
modified HPSNR and added SSIM MSSIM

modified HPSNR (default HVS size)
and added new function (SSIM and MSSIM)
additional explanation for SSIM and MSSIM

additional explanation ( name of paper and  the Authors) for SSIM and
MSSIM
modified HPSNR

change input variable to standard deviation in HPSNR function
delete the comment

Delete the comments on pixkit project code (which are moved to wiki page
of yunfuliu/pixkit )
add halftoning function (ED and OD)

Modified ED: FloydSteinberg1976
add ED functions (Jarvis1976, Stucki1981, and ShiauFan1996)

add OD functions (Ulichney1987)
Modified ED function
Merge branch 'master' of https://github.com/yunfuliu/pixkit
modified exception description

change exception description for ED and OD functions
add DD functions

add DD functions (Knuth and Mese)
modified parameter

modified parameter in DD function
remove the comment

remove the comment in halftoning functions
modified function
add comp function

add comp function (DBSBTC2011)
modified function decription

modified function decription in DBSBTC2011
Merge remote-tracking branch 'origin/master'
improved halftone functions

improved halftone functions  for adaptive image sizes
modified IQA functions

modified MSSIM and new IQA function MS_SSIM
Merge branch 'master' of https://github.com/yunfuliu/pixkit
merge