Minor doc fixes.
More doc fixes.
Improved streamWithURL method.

**The ivar "url" has also been renamed to "_url". This should not affect you as if you are getting the url, you should be using the url property. Subclasses overriding the streamWithURL method may be affected but these should move to call the superclass first. This will make your subclasses more future-proof too. Only use the "_url" ivar if you really need to (almost never). Open an issue if you have any queries.**