Integrate some library functions

To be honest, neither the attributes() nor the hasAttribute() functions are very well thought out.  My reasons for wanting to get into this territory were threefold.

(1) I noticed that you could get and set an object's properties from within EDEN code but there was no way to distinguish between a property that had the undefined value explicitly assigned to it and a property name that the object didn't have.
(2) Many languages have dictionaries/associative arrays/hashtables/whatever you want to call them but EDEN doesn't.  Being classless, objects serve that purpose in JavaScript.  I had a construal where I was starting to venue into using lists that looked like ["key1", "value1", "key2", "value2",...] and thought it was a bit flaky and that JS-EDEN deserved proper associative arrays.
(3) I've been having vague thoughts about starting to build relational databases in JS-EDEN (hence the term "attributes" rather than "properties").  There's certainly precedent for it with EDDI in tkeden.  And I thought (dangerously) that piggybacking on JavaScript's existing key-value mapping mechanism (i.e. objects) might serve as the basis for implementing relational database tuples.

So far as objective (1) is concerned Object.keys is not the right construct because any properties declared in the object's prototype matter too.  But then for objective (3) the notion of inheriting attributes in an OOP fashion is a messy departure from the relational model.  I have some more code written elsewhere that includes an explicit Tuple prototype, thus providing an appropriate toString() method and also a way of limiting the prototype chain to just one prototype, but I bottled out of uploading it to GitHub, partly because I discovered JS-EDEN's compact {key1: value1, key2: value2...} syntax.  This code is slightly simplified version of the original unversioned code.

Perhaps I should just delete this entire file from GitHub for now.  I've still got the original in an unversioned text file and I can create a branch if and when I get around to putting some serious effort into this little project.