[PROJ] Proj 6 API questions

[Even Rouault]

> I guess name should have a unique constraint if we were to guarantee unique
> names.

There is no guarantee that names are uniques, the EPSG database table 
declaration has no such guarantee itself, and we mix data from different 
authorities.
Only the tuple (auth_name, code) is guaranteed to be unique.
Actually in the proj.db, there are dupllicated names, like the following 
(after a fix I've just done since the code for the ESRI object was incorrect)

OGRFeature(SELECT):0
  auth_name (String) = EPSG
  code (String) = 1024
  name (String) = CGCS2000
  description (String) = (null)
  celestial_body_auth_name (String) = PROJ
  celestial_body_code (String) = EARTH
  semi_major_axis (Real) = 6378137
  uom_auth_name (String) = EPSG
  uom_code (String) = 9001
  inv_flattening (Real) = 298.257222101
  semi_minor_axis (Real) = (null)
  deprecated (Integer) = 0

OGRFeature(SELECT):1
  auth_name (String) = ESRI
  code (String) = 107038
  name (String) = CGCS2000
  description (String) = China Geodetic Coordinate System 2000
  celestial_body_auth_name (String) = PROJ
  celestial_body_code (String) = EARTH
  semi_major_axis (Real) = 6378137
  uom_auth_name (String) = EPSG
  uom_code (String) = 9001
  inv_flattening (Real) = 298.257222101
  semi_minor_axis (Real) = (null)
  deprecated (Integer) = 1

Even

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