Add symmetric option for overlap
Add symmetric option for overlap

poolio/thunder,jwittenbach/thunder,broxtronix/thunder,j-friedrich/thunder,oliverhuangchao/thunder,j-friedrich/thunder,kunallillaney/thunder,mikarubi/thunder,kcompher/thunder,pearsonlab/thunder,broxtronix/thunder,zhwa/thunder,zhwa/thunder,mikarubi/thunder,pearsonlab/thunder,poolio/thunder,kunallillaney/thunder,thunder-project/thunder,oliverhuangchao/thunder,kcompher/thunder