v0.1
   first version

v0.2
   handles .gz files, processing gunzip -c output through a pipe
   handles date overlap
   examines 'CCSM modification tag' to detect change of units in SFWF & RESID_S
   handle additional blank lines in read_tavg_names (stay backwards compatible)
   handle date format change in 'Global Time Averages' line (stay backwards compatible)
   change some units and put in corresponding scale factors

v0.3
   make compatible with POP2.0 log files