POC search
refactor to KV.from_listing
refactor to SearchResults
refactor to enumerable
SearchResults#take
SearchResults#offset

I thought about using #drop for this, but that will go ahead and the
enumeration before we can call #take; Then I thought about overloading #drop to
just set the offset and return the SearchResults object, but that breaks
Enumerable.  So, this.  One could argue that perhaps #take should be the same
thing for consistency, but I see #take being the more common use case and want
to optimize for that.
docs for SearchResults
fix docs
remove warning from docs build
[#61] Object client PUT relations
[#61] Relations delete
[#61] Very basic relation enumeration

It's a starting point, but still needs:

- Sub-relation querying
- better testing/handling of items outside of main item's collection
[#61] Better tests for kv from other collections
[#61] Allow graph traversal to arbitrary depth