Add crude support for plural elements; fix mixed content storage
Add crude support for plural elements; fix mixed content storage

CantemoInternal/pyxb,jonfoster/pyxb2,pabigot/pyxb,CantemoInternal/pyxb,balanced/PyXB,jonfoster/pyxb1,jonfoster/pyxb1,jonfoster/pyxb-upstream-mirror,jonfoster/pyxb2,balanced/PyXB,jonfoster/pyxb-upstream-mirror,pabigot/pyxb,CantemoInternal/pyxb,balanced/PyXB,jonfoster/pyxb-upstream-mirror,jonfoster/pyxb2