Need a better organization for the naming sections

[mkavulich]

Currently section naming hierarchy of the standard names looks like this:

base_names
  generic_names
  chemical_species
  base_standard_names
dimensions
constants
coordinates
state_variables
land_surface
diagnostics
atmospheric_composition
atmospheric_composition: GOCART aerosols
atmospheric_composition: GLOMAP/UKCA aerosols
emissions
Application-specific variables
  required framework-provided variables
  optional framework-provided variables
system variables
GFS_typedefs_GFS_control_type
GFS_typedefs_GFS_interstitial_type
GFS_typedefs_GFS_tbd_type
GFS_typedefs_GFS_sfcprop_type
GFS_typedefs_GFS_coupling_type
GFS_typedefs_GFS_statein_type
GFS_typedefs_GFS_cldprop_type
GFS_typedefs_GFS_radtend_type
GFS_typedefs_GFS_grid_type
GFS_typedefs_GFS_stateout_type

As you can see, it is a bit all over the place. Beyond the "base names" section and subsections, which are recent additions, there is little rhyme or reason to the naming of the sections, and even worse, the vast majority are grouped in an obscure GFS-specific way, which is not very useful for people attempting to browse/find existing names.

We should come up with a system of organization that can encompass all existing and potential future names, avoiding references to specific applications except when absolutely necessary.