To accomplish this, also
* implements `OneOf` union types
* passes desired return typing strategy to behavior factory functions
* adds formerly missing BooleanT utils
* adds isInteger utility function, along with its dependency isfinite
* adds several new and formerly missing Complex utils
In addition, it adds several Complex tests, including careful checking
of the behavior and return type of `math.cis` under different
`math.config.returnTyping` settings.
* Adds the concept of, and options for, the return typing strategy
* adds the strategy at the beginning of every behavior index
* adds the strategy as an additional argument to resolve
* No actual use of return type strategy so far
* Sets up eslint
* Fixes eslint errors
