Print out objects that exist but that aren't reachable from any
of the reference nodes.
---dangling::
---no-dangling::
+--[no-]dangling::
Print objects that exist but that are never 'directly' used (default).
`--no-dangling` can be used to omit this information from the output.
a blob, the contents are written into the file, rather than
its object name.
---progress::
---no-progress::
+--[no-]progress::
Progress status is reported on the standard error stream by
default when it is attached to a terminal, unless
--no-progress or --verbose is specified. --progress forces