Deprecate pat::Match and related

[CasualX]

This API was originally required to make the pattern scanner work with the Iterator trait (you cannot put the result of the iteration inside the iterator object, aka streaming iterator).

However this required that the returned object either had a fixed size (pat::MAX_SAVE) or a dynamically allocated Vec. So I went with pat::Match, a fixed length result object.

Since I've decided to drop the Iterator trait, the above workaround is no longer necessary and I would like to get rid of it.

Unfortunately #[deprecated] is very noisy so I expect this PR to remain until something changes, see rust-lang/rust#47219 and others.

[CasualX]

I'm going to close this because #[deprecated] is just too noisy, perhaps I should just remove it. This API can be reintroduced when streaming iterators are in std.