eval: add r5js.valutil.toJson, but do not use yet.
io+misc: simplify r5js.OutputPort by requiring r5js.JsonValue serialization.
eval+misc: get r5js.Evaluator back down to one method by using r5js.JsonValue.
eval+test: bring the "hasStringValue" tests back online.
test/matchers: break out have(String|Js)Value into their own files.
eval+test: bring more js interop tests back online.
test+io: bring some of the js interop output tests back online.