Added parsing for server commands, and moved it into api.

Sample slave bot is not really a thing anymore, since most functionality has been moved into `api.c` and `handlers.c`. `decode_chat_json` has been upgraded to allow server commands, i.e "/say \slot 8" from the server CLI.
Add a note saying `msg` and `sender_name` are malloced by `decode_chat_json`?
Also, aren't we habitually using 'calloc' instead?