[thredds] announce: netcdf-java and thredds 4.3.21 stable release

The Netcdf-Java library and TDS stable release 4.3.21 is now ready:

  
http://www.unidata.ucar.edu/software/thredds/current/netcdf-java/documentation.htm
  http://www.unidata.ucar.edu/software/thredds/current/tds/TDS.html

This release fixes a bug when reading netcdf-4 chunked files.