Addded Examples for $pull'ing Objects

There wasn't any documentation on how to `$pull` a specific entry
in an array of objects.

I've added a couple examples showing how you can do so.  I'm
not 100% about the `$gte` example, but I'm 99% sure that is
correctly done.

Signed-off-by: kay <kay.kim@10gen.com>
tweak pull example for array of documents