bots: Move contrib_bots to api/bots*.

This will make it convenient to include these bots in Zulip API
releases on pypi.

Fix #5009.

api/bots/encrypt/encrypt.py

@@ -0,0 +1,45 @@
+def encrypt(text):
+    # This is where the actual ROT13 is applied
+    # WHY IS .JOIN NOT WORKING?!
+    textlist = list(text)
+    newtext = ''
+    firsthalf = 'abcdefghijklmABCDEFGHIJKLM'
+    lasthalf = 'nopqrstuvwxyzNOPQRSTUVWXYZ'
+    for char in textlist:
+        if char in firsthalf:
+            newtext += lasthalf[firsthalf.index(char)]
+        elif char in lasthalf:
+            newtext += firsthalf[lasthalf.index(char)]
+        else:
+            newtext += char
+
+    return newtext
+
+class EncryptHandler(object):
+    '''
+    This bot allows users to quickly encrypt messages using ROT13 encryption.
+    It encrypts/decrypts messages starting with @mention-bot.
+    '''
+
+    def usage(self):
+        return '''
+            This bot uses ROT13 encryption for its purposes.
+            It responds to me starting with @mention-bot.
+            Feeding encrypted messages into the bot decrypts them.
+            '''
+
+    def handle_message(self, message, client, state_handler):
+        bot_response = self.get_bot_encrypt_response(message)
+        client.send_reply(message, bot_response)
+
+    def get_bot_encrypt_response(self, message):
+        original_content = message['content']
+        temp_content = encrypt(original_content)
+        send_content = "Encrypted/Decrypted text: " + temp_content
+        return send_content
+
+handler_class = EncryptHandler
+
+if __name__ == '__main__':
+    assert encrypt('ABCDabcd1234') == 'NOPQnopq1234'
+    assert encrypt('NOPQnopq1234') == 'ABCDabcd1234'