Include issues without project or milestone on boards.

In order to help organize issues, show issues on boards even if they
don't have an assigned project or milestone.

Refactor the issue hiding feature (using the `hide-until` property) to
be an option to IssueFilter rather than a separate, special-case. This
means that the CLI always filters by default.

Hide issues in the Done state on project boards unless the new
`--show-done` arg is passed.

pit.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version       = "4.31.0"
+version       = "4.31.1"
 author        = "Jonathan Bernard"
 description   = "Personal issue tracker."
 license       = "MIT"