Remove .then() requirement for basic library, cache API configuration

[tadman]

The dynamic method for pulling down the API configuration should be optional. Right now it's a mandatory initialization step which slows down the first API call made on any connection.

Caching it in the NPM module itself as well as allowing an alternate definition to be used would help with performance. Switching to dynamic mode as an option would not be a bad thing as that will allow easy upgrading to new API specifications.