Restructure contrib_bots bots to new layout.

In order to make the layout of all bots consistent, this commit
moves each bot into a folder with its name and modifies 'run.py'
so that only bots with such a structure can be executed. 'lib'
gets renamed to 'bots'.

contrib_bots/bots/followup/followup.py

@@ -0,0 +1,51 @@
+# See readme.md for instructions on running this code.
+
+class FollowupHandler(object):
+    '''
+    This plugin facilitates creating follow-up tasks when
+    you are using Zulip to conduct a virtual meeting.  It
+    looks for messages starting with '@followup'.
+
+    In this example, we write follow up items to a special
+    Zulip stream called "followup," but this code could
+    be adapted to write follow up items to some kind of
+    external issue tracker as well.
+    '''
+
+    def usage(self):
+        return '''
+            This plugin will allow users to flag messages
+            as being follow-up items.  Users should preface
+            messages with "@followup".
+
+            Before running this, make sure to create a stream
+            called "followup" that your API user can send to.
+            '''
+
+    def triage_message(self, message, client):
+        original_content = message['content']
+
+        # This next line of code is defensive, as we
+        # never want to get into an infinite loop of posting follow
+        # ups for own follow ups!
+        if message['display_recipient'] == 'followup':
+            return False
+        is_follow_up = (original_content.startswith('@followup') or
+                        original_content.startswith('@follow-up'))
+
+        return is_follow_up
+
+    def handle_message(self, message, client, state_handler):
+        original_content = message['content']
+        original_sender = message['sender_email']
+        new_content = original_content.replace('@followup',
+                                               'from %s:' % (original_sender,))
+
+        client.send_message(dict(
+            type='stream',
+            to='followup',
+            subject=message['sender_email'],
+            content=new_content,
+        ))
+
+handler_class = FollowupHandler