add possibility to manage manually a connection with pool feature

[Drazke]

Issue #284

New function :

db.driver.createPool(cb) --> return connectionId;
db.driver.releasePool(connectionId);

Updated function :

Model.create(data, connectionId, cb)
Instance.useConnection(connectionId).chainFunction()

[dxg]

Looks pretty good, thanks.
@dresende what do you think?

[dresende]

If it doesn't break anything, it's all good to me 👍

[dada-net]

SELECT ... FOR UPDATE

Model.find().where("id = 1 FOR UPDATE").run(function(err, result){
...
});

in transaction i want to lock by select
is method useConnectionId can't use in model ?
@Drazke @dxg @dresende

[Ottunger]

@Drazke @dresende Any update on this one, should it reach npm or should I check it out locally?
Same question for dresende/node-orm-transaction#6