[PROJ] Future maintainance releases

[Even Rouault]

> No, not at all. My concern is, or was, that a 6.3 version would be rather
> short-lived with a release of 7.0 only a few months later.

Depending on how much time it might take for 7.0 to be deployed to users using 
binary distribution channels, we might have to maintain a 6.x for some time.

> But if the
> changes you are proposing really are so disrupting I agree that it will be
> beneficial with a new minor-version release. I have one question though.
> Would it be a benefit to your work on vertical transforms if you were not
> restricted by the old API? The grid code is somewhat entangled as far as I
> remember and wouldn't be surprised if some of olde API functions is in the
> way of the smartest way to do things. If that is the case then I think we
> should just go straight to 7.0. If you can accomplish your work without
> working around the existing API a 6.3 release is fine with me.

For now, I'm most dealing with metadata related work, nothing in the grid 
handling itself. If the CDN related work happens to be done, yes it will be 
internally disruptive, but looking quickly at proj_api.h, I'm not even sure 
the old API would be a problem for that. The only thing that is grid related 
is pj_apply_gridshift(), but I don't think that would be an issue, and looking 
in Debian archive for
https://codesearch.debian.net/search?q=pj_apply_gridshift 
I can only find mentions of it in PROJ itself or its embedded copies by other 
projects, so basically no one in the open world is using it.

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