Instead of instructing users to do static calls
in to Unleash, she should instead be allwed to
specify the log provider as an option to Unleash.
This commit introduces the "getLogger" option,
a function responsible for creating a logger.
We use intervals in three places and we could probably organise them
better in the future. As long as they all do unref they do not form
any issues for us and I will just let them be as is for now.
This closes#186