added yaxs='o' feature for a single buffer
added yaxs='o' feature for a single buffer

jread-usgs/gsplot,lindsaycarr/gsplot,ldecicco-USGS/gsplot,jread-usgs/gsplot,aappling-usgs/gsplot,dpattermann-usgs/gsplot,dpattermann-usgs/gsplot,USGS-R/gsplot,jiwalker-usgs/gsplot,jiwalker-usgs/gsplot,thongsav-usgs/gsplot,lindsaycarr/gsplot,thongsav-usgs/gsplot,aappling-usgs/gsplot,ldecicco-USGS/gsplot