Make send-message work for existing chats with the bot.

I made a request on how to use send-message on the 40-ants gitter-chat, and a few steps were mentioned that would allow send-message to work correctly.

The steps that are mentioned are:

1. Make sure send-message is exported from the cl-telegram-bot/message package instead of cl-telegram-bot/bot (I see some other functions also need such refactoring.

2. Remove export of the make-chat function because now it waits some internal plist with response from telegram server.

3. Add another function make-private-chat which can be used to recreate chat object from remembered (in a database) chat_id, nickname and other params.

I plan to address each of these in this issue. I hope to not make more work for you.

Thank you for this project.