Added find_and_modify and some extra update logic.
Added find_and_modify and some extra update logic.

mdomke/mongomock,vmalloc/mongomock,marcinbarczynski/mongomock,StarfishStorage/mongomock,drorasaf/mongomock,optimizely/mongomock,magaman384/mongomock,julianhille/mongomock,akun/mongomock,chartbeat-labs/mongomock