Enhancement - #326

- Added feature #326, allowing tasks to be added in the completed state,
  by using the 'log' command in place of 'add' (thanks to Cory Donnelly).
- Added log command to task.1 man page.
- Added log command to task-tutorial.5 man page.
- Added log command to help text.
- Added log command unit tests.

src/report.cpp

@@ -77,6 +77,10 @@ int shortUsage (std::string &outs)
   table.addCell (row, 1, "task add [tags] [attrs] desc...");
   table.addCell (row, 2, "Adds a new task.");
 
+  row = table.addRow ();
+  table.addCell (row, 1, "task log [tags] [attrs] desc...");
+  table.addCell (row, 2, "Adds a new task that is already completed.");
+
   row = table.addRow ();
   table.addCell (row, 1, "task append [tags] [attrs] desc...");
   table.addCell (row, 2, "Appends more description to an existing task.");