Enhancement - Custom report limit override

- If a custom report has a specified limit to the number of tasks
  it shows, then that limit may be  overridden by specifying a new
  quantity on the command line.
- Added unit tests to verify expected behavior.
- Updated documentation to reflect new functionality.
- Removed obsolete documentation references to an "oldest" and
  "newest" configuration variable.

html/task.html

@@ -159,6 +159,9 @@
                   <li>Fixed bug that added an extra line between header and graph in the
                       ghistory report.
                   <li>Added simple 'taskprogram' mailing list subscribe form to the web site.
+                  <li>For custom reports that define a "limit" to the number of rows of output
+                      such as "oldest" and "newest", task allows an override value.  For
+                      example "task oldest 5" will display the 5 oldest tasks.
                 </ul>
 
                 <p>