Add @Created and @Updated annotations to Entity define

[zoujiaqing]

Add annotations:

1. Created : Get the timestamp automatically at creation time.
2. Updated : Get the timestamp automatically at update time.

Sample code:

import hunt.entity;

class User
{
    @PrimaryKey
    int id;

    string name;

    @Created
    int created;

    @Updated
    int updated;
}