Allow authorities other than EPSG in GeoTIFF#121

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Geomatys:TestBed-19/AlternativeAuthorities

Commits on Sep 19, 2023

In table E.1 (Summary of GeoKey IDs and names), move the `CoordinateEpochGeoKey`
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Break long sentences in shorter sentences in sections 7.2.2, 7.5, B.3 and requirement 16.5.
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Introduce TextDefGeoKey for textual definitions of the following forms:
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