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/help/help.py

@@ -0,0 +1,39 @@
+# See readme.md for instructions on running this code.
+
+class HelpHandler(object):
+    def usage(self):
+        return '''
+            This plugin will give info about Zulip to
+            any user that types a message saying "help".
+
+            This is example code; ideally, you would flesh
+            this out for more useful help pertaining to
+            your Zulip instance.
+            '''
+
+    def triage_message(self, message, client):
+        # return True if we think the message may be of interest
+        original_content = message['content']
+
+        if message['type'] != 'stream':
+            return True
+
+        if original_content.lower().strip() != 'help':
+            return False
+
+        return True
+
+    def handle_message(self, message, client, state_handler):
+        help_content = '''
+            Info on Zulip can be found here:
+            https://github.com/zulip/zulip
+            '''.strip()
+
+        client.send_message(dict(
+            type='stream',
+            to=message['display_recipient'],
+            subject=message['subject'],
+            content=help_content,
+        ))
+
+handler_class = HelpHandler