async callback

[PauloASilva]

Hi, Do you consider to refactor the validate async callback to be according Node.js callback pattern as it would allow Promises?

By now I'm using a workaround

var Q = require('q');
var JaySchema = require('jayschema');
var js = new JaySchema();

js._validate = function(instance, schema, callback) {
    js.validate(instance, schema, function(err){
        callback(err, instance);
    })
}

Q.nfcall(js._validate, req.body, schema)
    .then(function(data){
        // validation success
    })
   .catch(function(err){
       console.log(err);
   })
;