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.

Example Link:
http://stackoverflow.com/questions/9048424/removing-specific-items-from-array-with-mongodb