Compare the new ES6 spread operator with the traditional concat() method

Comparing different methods of looking up values keyed by a mixture of string and number keys, for a small number of entries. Used to make decisions about how to cache reverse enum key lookups in ts-enum-util: https://github.com/UselessPickles/ts-enum-util

Comparing different methods for using an arbitrary object as a Map key, for a relatively small number of entries. Used to make decisions about how to cache WrappedEnum instances in ts-enum-util: https://github.com/UselessPickles/ts-enum-util