Allow documents to self-reference

gistfile1.py

class Doc(Document):
    structure = {
       "connections": [ SELF ],
       "some":  unicode,
       "other": unicode,
       "important": int,
       "data": uncode,
    }


a = db.test.Doc()
a.save()

b = db.test.Doc()
b.save()

c = db.test.Doc()
c.save()

a.connections = [ b, c ]
a.save()

b.connections = [ a, c ]
b.save()

# now:

s = a.connections[1].some
x = [ i.important for i in b.connections ]
x2 = db.test.Doc.find({ "connections": { "$in": [ b ] }})
#etc.