CompressionMethod and PhotometricInterpretation should be NonExhaustive

[HeroicKatora]

This is a small compatibility hazard, the only enum variants are the currently supported or introduced variants for these two (and potentially other) fields in tiff. Adding new variants breaks user code that matches on them, it would be customary to use instead an explicit __NonExhaustive variant that is not publicly documented and explicitely should not be matched against.

[HeroicKatora]

Tag could be non exhaustive as well. Adding detection for now tags, effectively moving from Unknown to a new known variant such as potentially suggested in #47, does not require a breaking change.