Changes to FileChangeObserver behavior to fix the race condition/loses focus repeatedly bug (Issue #239 and Issue #231) that occurs when the "automatically refresh task list from file" option is on. Also makes the "automatically refresh task list from file" option work as set without restarting the app.
Implemented changes that move focus to the top item in the task list (or to the listbox itself if no items are left in the task list) after items are deleted or archived. Closes Issue #239.
Modified archive method to retain selections in the task list after archiving. If all selected tasks are archived, move the selection to the top of the task list. Improves solution to Issue #239.
Closes Issue #244: SetTaskDueDate() doesn't work if the due date is at the start of the task.
Closes Issue #243: RemoveTaskDueDate() doesn't work if due date is at the beginning of the line.
Postpone to "Sunday" feature.

Allow user to postpone a task to a day, rather than number of days from
now.  So Postpone Sunday will postpone the task to next Sunday, rather
than requiring the count of days between now and Sunday.
Merge pull request #245 from Piscean/dev

Postpone to "Sunday" feature.
Fixed typo in Help text.  Added Help for Postpone.  Widened Postpone TXT entry field so "Wednesday" doesn't wrap.
Merge pull request #246 from Piscean/dev

Minor Help and Postpone fixes
Closes Issue #247: Changing filters causes loss of selection in task list.
Closes Issue #249: Bug: When there are duplicate tasks and one is selected, all get selected after sorting the task list.
Closes Issue #248: Bug: After editing a task, focus is not moved to the newly created or edited task.
This patch fixes a regression introduced in commit 645f572 (When duplicate tasks are selected, only one of those tasks retains selection after a sort, filter, or other operation). Closes Issue #249.
Closes Issue #250: Bug: When reloading the todo.txt file, task list selections are lost.
Closes Issue #252: Bug: After updating Options, task list selection is lost. Ensures that, after Options are set, the task list is refreshed only if options related to its display are changed. Those options are: "Current Font" (any font attributes), "Allow grouping of tasks", and "Filter text is case-sensitive".
Closes Issue #251: Bug: Pressing the Esc key in the text box causes focus to move to menus, etc.
Closes Issue #225: Bug: Priority (Z) sorts below No Priority (n/a).
Fix for Postpone to Tuesday bug where "Tuesday" didn't equal "tuesday".
Merge pull request #255 from Piscean/dev

Fix for Postpone to Tuesday bug where "Tuesday" didn't equal "tuesday".
Release 3.1.0