0.6.0-rc1: This a Release Candidate which is based on a good number of changes

which are in `master` branch and might still be released as 0.5.1
release.  Those changes are yet to be documented.

Added
- `download` now can download from "published" (versioned) dandisets.
  The entire `download` was refactored and new UI also uses pyout (as
  `upload` and `ls`) so there will be no tqdm progress bar indicators.