Database

2 Tables

Settings
Int, String, String
Id, Identifier, DefaultValue

GuildSettings
Id, GuildId, SettingId, Value

Code

Needs a public interface so cogs can register settings for themselves
e.g.
register_setting("christmasMode", "false")

When pulling a setting, if no entry for the guild, use default value.
GuildSettings entry only exists once it has been explicitly set.