test: correct name of a static field
boot: put I/O state in r5js.EvaluatorImpl, not r5js.Pipeline.
test matchers: use instance state where possible in evaluates_to.js.
io: add r5js.OutputSavingPort for use in testing output from JS.
eval: add r5js.Evaluator#withPorts + impl.
runtime: temporary fix for write impl.
test: add matcher for testing output port outputs.
eval: improve return type of r5js.ToJsEvaluator#schemeToJsValue_.
test: add basic output test.