A few things I've wanted as I do PM, plus some changes for later automation via
probot:

* Drop `Enhancement` -- it vaguely implies "new feature"
* Instead use `Feature` for new **accepted** and on our roadmap features
* If an issue doesn't describe a bug, and is not a new feature, it's likely an
  Improvement. The distinction here is `Feature` is a new feature, `Bug`
  has higher priority than `Improvement`
* `Needed: more information` is a way to track issues that require a reply and
  can be closed if we don't get that reply. Currently, we use this in some
  places as a way to describe issues that we need to collect more ideas on --
  a good substitute is `Needed: design decision`
* Also add `Status: stale` for issue automation
* Drop unused statuses for closed issues
* Drop PR: ready as this is a leftover from before GH had reviews
* Drop `Feaure Overview`, this is synonymous with `Feature`

The takeaway here for purposes of what to audit with these changes in place:

* If an issue is an `Enhancement` now:
  * It becomes a `Feature` if it is a new feature and belongs on our roadmap
  * It becomes an `Improvement` if it is not a bug and belongs on our roadmap
  * It gets closed otherwise, it's not important to us
* Issues that are `Needed: more information` can be closed if there was no reply
  after 7 days. We might need to retriage some issues where this label was
  applied for another reason

Also, suggestions for alternatives to `Improvement` are helpful, if this isn't
descriptive enough.

Priority: high already exists in rtfd/readthedocs.org. Matching low priority for
extra use as well.