Add one function (get_bot_botname_response()) that generates response
from the given input and replies back to the handle_message with the final
content of response to be sent. Also add code to bots(except followup) to
reply to private messages along with stream messages.
To make all bots consistent add shared function in bot_lib.py
to check if this bot is called. All bots respond to at-mention of
the bot instead of their specific names.
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'.
