Enhancement - annotations

- Added support for "annotate" command to annotate existing tasks.
- Bumped file format to version 3, due to the annotations.
- Added unit tests to verify that annotations work.
- Changed 'description' column everywhere to include annotations.
- Added 'description_only' column to exclude the annotations.
- Fixed bug in Table.cpp that calculated the width of multi-line
  columns by using the cell length, instead of the length of the
  longest individual line.
- Updated documentation with new feature.
- Updated documentation with new column.
- Enhanced t.t unit tests to cover format 43

src/Config.cpp

@@ -171,6 +171,7 @@ void Config::createDefault (const std::string& home)
 
         // Custom reports.
         fprintf (out, "# Fields: id,uuid,project,priority,entry,start,due,recur,age,active,tags,description\n");
+        fprintf (out, "#         description_only\n");
         fprintf (out, "# Description:   This report is ...\n");
         fprintf (out, "# Sort:          due+,priority-,project+\n");
         fprintf (out, "# Filter:        pro:x pri:H +bug\n");