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.

ChangeLog

@@ -20,6 +20,9 @@
  + Fixed bug that added an extra line between header and graph in the
    ghistory report.
  + Added simple 'taskprogram' mailing list subscribe form to the web site.
+ + 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.
 
 ------ old releases ------------------------------