Setup baseline JSON response tests
Remove unused delimiter parameter to ease matching method signatures

Although this has never caused a PHP warning or error that I know of,
PHPUnit complained that the JSON response content method didn't match.
Migrate internal storage from pre-encoded JSON to data references

This will make collection of large amounts of data more efficient, as
well as simplify the process of adding content when using the class.
Remove extraneous comma from encoded value

Apparently the old implementation neglected to trim the trailing comma
on the unnamed collection.