look into making ObjectBuilder lazy on the right

[chadaustin]

I can't imagine a situation where this matters yet, but in case it comes up someday:

https://github.com/lpsmith/json-builder/commit/b33adc7c8a959cec918485900cc3c8360b23854d

Also http://blog.melding-monads.com/2012/02/24/implementing-json-builder-or-how-the-commabuilder-got-its-spots/