Add ability to handle and load an xml config

[plastikfan]

• [ ] Define synchronous config file load function
• [ ] Create synchronous config load tests
• [ ] Define async config file load function
• [ ] Create async config file load tests Branch: setup

[plastikfan]

Note, we can block on the outcome of a promise by using async. So once we create the promise to load the large xml config file, we async await on the created promise, then proceed.

See: await

[plastikfan]

First define synchronous version then add async version using promisify

[plastikfan]

Already fixed as part of feat #13.