Changes for /history function:
Changed chatroom structure for history
Added global constant HISTORY_SIZE (maximum history per chatroom)
Added new entry to commands array - CMD_HISTORY calls get_history
Added get_history function definition to print out the current chat room's history for the user
Updated init_chatroom function to initialize history lock (& not intialize history) so we don't get collisions
Updated write chatroom to copy the current message to the user's chatroom history
Updated remove_user_from_chatroom to remove history locks if chatroom is empty
Removed extra newline that was being printed when a user joined the chatroom (because it was weird in history)

Other misc changes:
Changed logout() calls in kick functions so it would compile
Replaced counter in process_command DEBUG_CMD block so you can turn on debugging without compiler errors