split #insert, refactor send_write, remove/delete with :limit

RUBY-676
Documentation for bulk write API and #remove with :limit opt

RUBY-676
#insert optim with respond_to? plus documentation tweak

RUBY-676
Merge branch '1.x-stable-ruby-676' of github.com:gjmurakami-10gen/mongo-ruby-driver into gjmurakami-10gen-1.x-stable-ruby-676
Merge branch '1.x-stable' of github.com:mongodb/mongo-ruby-driver into 1.x-stable