update variables page with new substitutable EXIF and GPS variables

[ralfbrown]

[elstoc]

Thanks @ralfbrown. Please can you remove the submodule update from this branch, and then I'm happy to merge.

[elstoc]

Actually no, this will have to wait until we've finalised the 4.8 updates so no hurry.

[ralfbrown]

I don't know how that happened, and when I tried pushing again after a submodule update, git told me everything is up-to-date and refushed to push....

[elstoc]

Yeah if you look at the commit, it thinks everything is the same, it's just a different commit hash. Maybe squash and rebase? If you can't fix it I'm happy to just rekey this stuff into a new branch when we start merging changes for 5.0

[ralfbrown]

I had already tried rebase followed by submodule update, but that indeed did not change the commit hashes. Squashing was successful.

[elstoc]

Hmm it still seems to think the submodule is updated. Shrug

[ralfbrown]

One more variable to add:

$(IMAGE.TAGS.HIERARCHY)    tags list, preserving hierarchy

Your call on whether to rename TAGS to the now-preferred IMAGE.TAGS or make a duplicate entry, since both are still in the autocomplete list.

[ralfbrown]

Superceded by 683.