Export commands deprecated

- Provided examplars of export commands re-implemented using the new
  _query command.
- Implemented export-xml.pl, export-xml.py, export-xml.rb.
- Implemented export-csv.pl.
- Implemented export-yaml.pl.
- Implemented export-ical.pl.

scripts/add-ons/export-xml.rb

@@ -0,0 +1,67 @@
+#! /usr/bin/ruby
+################################################################################
+## 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
+##
+################################################################################
+
+require 'rubygems'
+require 'json'
+
+# Use the taskwarrior 1.9.4+ _query command to issue a query and return JSON
+lines = IO.popen("/usr/local/bin/task _query " + ARGV.join(" ")).readlines
+
+# Generate output.
+print "<tasks>\n"
+lines.each do |line|
+  data = JSON.parse(line)
+  print "  <task>\n"
+  data.each do |key,value|
+    if key == "annotations"
+      print "    <annotations>\n"
+      value.each do |anno|
+        print "      <annotation>\n"
+        anno.each do |key,value|
+          print "        <#{key}>#{value}</#{key}>\n"
+        end
+        print "      </annotation>\n"
+      end
+      print "    </annotations>\n"
+    elsif key == "tags"
+      print "    <tags>\n"
+      value.each do |tag|
+        print "      <tag>#{tag}</tag>\n"
+      end
+      print "    </tags>\n"
+    else
+      print "    <#{key}>#{value}</#{key}>\n"
+    end
+  end
+  print "  </task>\n"
+end
+print "</tasks>\n"
+exit 0
+
+################################################################################
+