Add config.yaml dependency to rst files

Enables incremental Sphinx builds: an rst file is rebuilt
if a referenced yaml file has changed.

This should remove the need to use "make touchrst" in
A+ course builds because changes in exercise config.yaml files
should be detected even if no rst file has been changed.

Fixes apluslms/gitmanager#25

directives/ae_output.py

@@ -90,6 +90,8 @@ def run(self):
                 raise SphinxError('Missing config path {}'.format(self.options['config']))
             data = yaml_writer.read(path)
             config_title = data.get('title', None)
+
+            env.note_dependency(path) # Add the config file to the rst file's dependencies
         else:
             data = { '_external': True }
             if 'url' in self.options:

directives/submit.py

@@ -74,6 +74,8 @@ def run(self):
                 raise SphinxError('Missing config path {}'.format(self.options['config']))
             data = yaml_writer.read(path)
             config_title = data.get('title', '')
+
+            env.note_dependency(path) # Add the config file to the rst file's dependencies
         else:
             data = { '_external': True }
             if 'url' in self.options: