PR draft: #229
The implementation, docs and tests are done. But there are the following issues to discuss:

I'd remove pure/Queue, leaving pure/Deque as the only implementation. Why: Deque was available in the old base lib, minimal migration would be necessary. IMO 'Deque' is a better name than 'Queue' as it better conveys its functionality: a double-ended queue. Having both Queue and Deque modules is probably not worth it. Reply: Queue names were already announced on the forum, let's leave it at that
Preserving the order when traversing elements requires O(size) memory (because ~half of the elements are stored in reversed order in pure lists). Most notably forEach and equals need O(size) allocations. Other operations like contains, any and all use only O(1) space but they traverse the elements in arbitrary order. All of these aspects are described in the documentation of each function.

(pure) Queue is an amortized queue. Nipkow has non-amortized functional queue that may serve us better #149

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