Teach the library to automatically handle cursors

[ecaron]

Now that the search endpoint handles cursorMark, we should be able to introduce a cursor=true parameter, and then have the library automatically create a .next() function that continues to traverse the stack.

This would be preferred over the dirty way I threw together at https://gist.github.com/ecaron/1e4851492d58db66ef4c1ef53010234a

[Flet]

I think this is halfway covered by the newasStream functions, but its not quite.

Having something like result.next() would allow the next page of results to be called manually and could be useful for certain applications.

Leaving this open for now.