Feat commander

[apachano]

Adds a command registry and CLI interface.
The CommandBook is the registry that stores commands for use by a Commander. A Commander is constructed with a CommandBook and two streams (one in and one out) that can either be cin/cout for terminal use with the server or point to streams in the client (the chat terminal). The commander contains a loop that checks for input and executes commands.

The commanders have 3 built-in functions that don't exist in the CommandBook, these are hardcoded and can't be overwritten. A help function, a list function, and an exit function.

[vyomfadia]

Run a Clang format before the final merge, but the code seems good, just a few nitpicks I have. Get it compiling though! 😛

[DontBelieveMe]

In general, the code looks good :D but like beeper says if you could run clang-format on the changes, and address the few comments I've left - only little things so nothing major.

Overall though, good job 👍