Remove Promise dependency for Knit core

[Sleitnick]

Just use coroutines instead of promises. Light-weight and easier for users to understand. Promises a great, but a little overkill for what Knit is trying to accomplish on startup.

Another current issue is that promises can hide errors on Knit lifecycle methods, which have to be caught with :catch(). It is better to fail hard if an error comes up on startup.

[Sleitnick]

This will force a major version increment.