update ChangeLog, NEWS in prep for 2.1.0 release

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@11814 b70326c6-7e19-0410-871a-916f4a2858ee
forgot README.postgis

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@11815 b70326c6-7e19-0410-871a-916f4a2858ee