The response type holds represents the way a bot can respond to a
message it executes and allows us to move the IRC dependency out of
bot and into only the main module.
This commit creates a bunch of new modules that contain code and tests
for various concepts/implementations that used to exist inside
bot.zig.
Notable amongst these are:
- buffer.zig, which contain the circular buffer containing both
backlog and outbox messages.
- parser.zig, which contain the parser used to parse commands from IRC
messages.