AST-47 List functions in AS, inspired by SML Basis library

samples/collections/README.md

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+[See #127](https://github.com/dfinity-lab/actorscript/issues/127)
+
+Critical modules
+==================
+ - [x] **List**: See [`List` module from SML Basis library](http://sml-family.org/Basis/list.html).
+ - [ ] **Hashtrie**: Persistent maps, as functional hash tries.
+ - [ ] **Hashtable**: Mutable maps, as imperative hash tables.
+
+Secondary modules
+==================
+These modules _may_ be useful in the collections library:
+ - [ ] **Stream**: Type def done; most operations are pending...
+
+Other modules
+==================
+These modules are merely exercises (toys/examples), and _not_ essential to the collections library:
+ - [ ] **Thunk**: Type def and some operations are done.
+
+