Added sample documentation comments 

These comments were added to to include/builtins/map.k, include/builtins/set.k, and include/builtins/list.k. As autoinclude cannot currently be turned off, these modules will be present in any file kompiled with the option --backend-doc. 

These comments represent what I think would be helpful to users looking for general-purpose tools and information. The documentation for each builtin module should include a general description of the module, as well as information on usage that may not be mentioned explicitly in the module, such as user-defined lists. For any container sort, information on adding, removing, and updating elements should be present. 

These comments are based on what existing comments there were, which were sometimes cryptic. As I'm not an expert in internal implementations, these comments are spare, and should probably include information about potential misuse or common errors. These comments are meant to be an example and a starting point, not as authoritative and sufficient, and they should be updated by persons more knowledgeable about implementation and use.