Dynamic default value

[erfanium]

For example:

schema = {
   createdAt: {
      type: "date",
      default: () => new Date()
   }
}

I'll update README.md after approvement

[coveralls]

Coverage increased (+0.004%) to 99.577% when pulling d994d07 on date into 7427b83 on master.

[icebob]

Nice, could you add an example to the README, as well?

[icebob]

Thx