Use kellydunn's original go-art package.

We no longer provide an interior (non-leaf node) search for
suffix traversal. Also remove the unused radix tree from the
db.go implementation.
Remove unused datastructure
Fixes and data structure simplifications

Change to using ByteSize for index/data sizes.

Return just a pointer to Repo in the IndexResponse,
as we'll only ever create one (no need for the Repos
collection).

Test additions and fixes.
Update afind tool to new IndexResponse format
Remove unused module
Many improvements in readiness for live testing

* Add search metadata filtering
  When Meta is provided in a SearchRequest, each Repo being
  considered's metadata is matched against the request Meta
  and if the value matches or is not mentioned in the
  request, the Repo will remain in the search.

* All searches use the same response struct
  A search, whether on one or more repos, deserves the same
  structure to ease later merging.

* Much cleanup and remote search improvements

Todo: needs some work on 'afind repos' command and the -key option to
afind, as well as -help usage texts.