Revert #20 causing regression and add tests for reviver

[zalmoxisus]

As discussed in #24, it was introduced a regression in #20, so I think it's better to revert it. Additionally to handling references (as per #19), it's disabling stringifying of all special types, also decreases the performance adding another stringifying and because not using needsRetrocycle it will also add extra operations during parsing when not needed.

I'll look into #19 later, that could be already implemented in #7.

[zalmoxisus]

Looks like #7 is only removing circular references, but still adding references otherwise:

var obj1 = { a: 1 };
var obj = { "prop1": obj1, "prop2": { "prop3": obj1 } };
jsan.stringify(obj, null, null, {circular: '∞'});

It's returning

'{"prop1":{"a":1},"prop2":{"prop3":{"$jsan":"$.prop1"}}}'

So we'd need an additional option to disable adding references, but not sure if it will hang for circular structures in that case.

[zalmoxisus]

Merging this and adding refs option in 8021553.

[kolodny]

Thanks for looking into and fixing this