per-user command history

make sure that command history is tracked separately per every user that
talks to the bot
[ChatRoom] become Python 3 compatible

thanks to  https://github.com/oxplot/fysom/issues/1
which in turn references http://www.rfk.id.au/blog/entry/preparing-pyenchant-for-python-3/
HIDE_RESTRICTED_COMMANDS option added

if set to True in config will prevent restricted commands to appear in the help response
Add test for per-user command history
Fix bot not recognizing commands in a chat if prefix is optional
Add err-markovbot to built-in list of plugins

err-markovbot is (oh surprise) a markov chain bot you can
see at https://github.com/MaxWagner/err-markovbot
Because no chatbot is complete without a markov chain.
added the new version checker to support suffixes
v2.0.0 beta preparation
rst fixups