ENH:  Add Kmeans thresholding option.
ENH:  Add Kmeans thresholding option.

stnava/ANTs,stnava/ANTs,stnava/ANTs,fbudin69500/ANTs,dawnsong/ANTs,fbudin69500/ANTs,dawnsong/ANTs,stnava/ANTs,stnava/ANTs,fbudin69500/ANTs,dawnsong/ANTs,dawnsong/ANTs,dawnsong/ANTs,stnava/ANTs,dawnsong/ANTs,fbudin69500/ANTs,stnava/ANTs,fbudin69500/ANTs,fbudin69500/ANTs,dawnsong/ANTs,fbudin69500/ANTs