Allow passing custom (querystring) parsing module(s)

[tunnckoCore]

By default to use querystring, but it can be done to use qs passed from options for example. This would be the easiest fix for the querystring issues.

[tunnckoCore]

What irony, haha.

Actually, I'm thinking that for that about months and that Octet and JSON parsers could be done better.

@felixge actually why they are "custom streams" e.g. event emitters with .write and .end methods? Because the need for more stable 0.10 support?

And actually what you think about dropping Node < 4 support? /cc @felixge @pornel @badeball

[felixge]

@tunnckoCore I don't know what you mean by `custom streams. When I wrote this module, these were the only kind of streams that existed ;).

I'm also the wrong person to ask about dropping Node < 4 support. I don't know if that's a reasonable thing to do these days.

[tunnckoCore]

dropping < 4 support will allow using more stable and "real" streams using the stream module instead of eventemitter.

i said "custom streams", because streams are event emitters, but eventemitters are not streams. and so i believe these parsers can be transform or write streams.