Flatten configuration further

[udoprog]

Completely remove [[irc.channel]] in favor of a [irc] channel argument.

Move currency configuration to root of config.

We can now only configure the bot to be present in a single channel.

[udoprog]

New configuration (including currency) will go from this:

[irc]
bot = "setmod"
moderator_cooldown = "5s"
# whether to notify when viewers are rewarded with loyalty currency.
notify_rewards = false

[[irc.channels]]
name = "#setbac"
currency = {name = "ether"}

To this:

[irc]
bot = "setmod"
channel= "#setbac"
moderator_cooldown = "5s"
# whether to notify when viewers are rewarded with loyalty currency.
notify_rewards = false

[currency]
name = "ether"