Columns - mask, imask, parent

- Implemented column objects for the mask, imask and parent attributes.
  Why not.

src/columns/ColMask.cpp

@@ -0,0 +1,83 @@
+////////////////////////////////////////////////////////////////////////////////
+// taskwarrior - a command line task list manager.
+//
+// Copyright 2006 - 2011, Paul Beckingham, Federico Hernandez.
+// All rights reserved.
+//
+// This program is free software; you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free Software
+// Foundation; either version 2 of the License, or (at your option) any later
+// version.
+//
+// This program is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+// details.
+//
+// You should have received a copy of the GNU General Public License along with
+// this program; if not, write to the
+//
+//     Free Software Foundation, Inc.,
+//     51 Franklin Street, Fifth Floor,
+//     Boston, MA
+//     02110-1301
+//     USA
+//
+////////////////////////////////////////////////////////////////////////////////
+
+#define L10N                                           // Localization complete.
+
+#include <math.h>
+#include <Context.h>
+#include <ColMask.h>
+#include <text.h>
+#include <i18n.h>
+
+extern Context context;
+
+////////////////////////////////////////////////////////////////////////////////
+ColumnMask::ColumnMask ()
+{
+  _name       = "mask";
+  _type       = "string";
+  _style      = "default";
+  _label      = STRING_COLUMN_LABEL_MASK;
+  _modifiable = false;
+
+  _styles.push_back ("default");
+
+  _examples.push_back ("++++---");
+}
+
+////////////////////////////////////////////////////////////////////////////////
+ColumnMask::~ColumnMask ()
+{
+}
+
+////////////////////////////////////////////////////////////////////////////////
+bool ColumnMask::validate (std::string& value)
+{
+  return true;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Set the minimum and maximum widths for the value.
+void ColumnMask::measure (Task& task, int& minimum, int& maximum)
+{
+  minimum = maximum = task.get ("mask").length ();
+
+  if (_style != "default")
+    throw format (STRING_COLUMN_BAD_FORMAT, _name, _style);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void ColumnMask::render (
+  std::vector <std::string>& lines,
+  Task& task,
+  int width,
+  Color& color)
+{
+  lines.push_back (color.colorize (task.get ("mask")));
+}
+
+////////////////////////////////////////////////////////////////////////////////