Adds text property size option

Allows people to do:

```js
db.define('person', {
  name: { type: "text", size: 50 } // VARCHAR(50)
});
```
Changes sqlite date type to text, it has no datetime type

Driver needs to use the builtin functions to convert from/to date
Adds mysql/postgres support for date-only types

Se `time: false` to date property to avoid storing times
Changes sqlite date type back to datetime

Is seems sqlite accepts datetime as an affinity to numeric
Adds unsigned option to number property