Fix quotedExpr parsing

So, now we actually parse quoted things. Their type is, roughly (written in HtDP style):

    [JSArray ParsedSingletonExpr]

where ParsedSingletonExpr is the return type of `parseExprSingleton`. This still seems a bit odd, since parseExprSingleton doesn't do anything special to symbols or literals, their lexemes are just inserted. We end up with things like:
```javascript
new quotedExpr([new literal(1), ["quasiquote", "hi"]])
```
which doesn't seem quite right. It's not clear what data type should be in the argument to quotedExpr. In some sense, leaving the "quotedExpr" constructor at the outer most later says to me that the pieces under it haven't yet been turned into data. Which is to say, we view them as uninterpreted, but parsed, expressions. By comparison, the expression 
```scheme
'(1 `hi)
```
could be parsed as
```javascript
new callExpr(new idExpr("list"), [new literal(1), new symExpr("hi")])
```
where I just invented `idExpr` and `symExpr` because I'm not sure to what they correspond in the code base. I think quotedExpr might actually be used to refer to both symbol data as well as quoted data (note that quoted identifiers correspond exactly to symbol data).


Anyway, right now we have something that seems partially correct. I added a hack to quotedExpr.toString to ensure that things look "right" in the string form.

To be certain of the implementation, I need to know the input-type/interface of `compile` so I can produce what `compile` expects.