Support custom jinja2 filters.

This uses the plugin framework to add filter plugins.
The previously hardcoded core filters are defined using the plugin
framework now.

examples/playbooks/custom_filters.yml

@@ -0,0 +1,6 @@
+---
+
+- name: Demonstrate custom jinja2 filters
+  hosts: all
+  tasks:
+  - action: template src=templates/custom-filters.j2 dest=/tmp/custom-filters.txt

examples/playbooks/filter_plugins/custom_plugins.py

@@ -0,0 +1,29 @@
+# (c) 2012, Jeroen Hoekx <jeroen@hoekx.be>
+#
+# This file is part of Ansible
+#
+# Ansible 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 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible 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 Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+class FilterModule(object):
+    ''' Custom filters are loaded by FilterModule objects '''
+
+    def filters(self):
+        ''' FilterModule objects return a dict mapping filter names to
+            filter functions. '''
+        return {
+            'generate_answer': self.generate_answer,
+        }
+
+    def generate_answer(self, value):
+        return '42'

examples/playbooks/templates/custom-filters.j2

@@ -0,0 +1 @@
+1 + 1 = {{ '1+1' | generate_answer }}