[wip/rfc] Cleanup Close.io

[sperand-io]

Dry's up the Close.io handler code considerably.

IMO, we should be demonstrating and advocating the power and concision of ES6 (of which TS is a superset, for future state...)

• spread operators
• template literals
• destructuring
• object property value shorthands and dynamic property keys

...and of more functional approaches to iteration and string/collection manipulation, such as map, reduce etc.

Generally, less branching control flow = easier to follow!

Thoughts? @markhazlett @nzoschke