Preserve indentation in multi-line list entry

[JelleZijlstra]

I would like to put this in a NEWS entry:

The following `threading` methods are now deprecated and should be replaced:

- `threading.activeCount` => :func:`threading.active_count`

- `threading.Condition.notifyAll` =>
    :meth:`threading.Condition.notify_all`

But when blurb generates the NEWS file, it produces:

- bpo-43723: The following `threading` methods are now deprecated and should
  be replaced:

  - `threading.activeCount` => :func:`threading.active_count`

  - `threading.Condition.notifyAll` =>
  :meth:`threading.Condition.notify_all`

Which is invalid rst, because the second line of the list is not indented enough.

It's because blurb uses textwrap.wrap to reflow the text, and that function eats any leading space in the line. Fixing this might require doing something more RST-aware.