[ANN] Rebellion collection libraries: multisets, multidicts, and association lists, oh my!

[Jack Firth]

The rebellion package recently acquired a few new collection libraries:

• rebellion/collection/multiset - A library for multisets, which are like sets that can contain duplicate values
  
• rebellion/collection/multidict - A library for multidicts, which are like hashes from keys to sets of values
  
• rebellion/collection/association-list - A library for association lists, which are like hashes from keys to lists of values
• rebellion/collection/entry - A small supporting library that defines an (entry key value) struct, in order to make it clearer when a pair is being used as a key-value mapping rather than as an arbitrary pair

All of the new collection types are immutable, but they don't (yet) support efficient persistent updates (e.g. there's no multiset-add function yet). These libraries are currently in early alpha versions, so not much beyond the basics is implemented and their APIs might change without warning. Let me know what you think and please feel free to file feature requests and bugs in the rebellion github repository!