Version 0.2
 - NetCDF4 groups and UDTs
 - var.get.nc with fitnum == TRUE
 - Write NetCDF files


Future
 - Analyze if sources belong together
 - Select slice of data with `[`, tidyverse style
 - More CF
 - Testing


THREDDS
https://thredds.aoos.org/thredds/dodsC/AOOS_GAK_ROMS_BGC_V2_MONTHLY_DIAG.nc
