[[NotSpam Email:998114491]] SRecordInstance inheritance support

Hi, 

For inheritance, SQL 99 native inheritance is flawed or not present in most datase. So i decided to implements it in the orm instead.  flatten the subtypes out, is not practical for commons use of inheritance because of limitations of columns names, and ugly sql table. Also flattening, its not easy to know which record is a simple Person and which is an Employee. Example of use :  module1 declare Person and module2 declare Employee.  An Employee is a Person so its should be retrieved in Person find call, but not as Person type but as Employee extends Person type.

I'm not so familiar to SimpleORM but i'll get to be. I'm using Test-driven approach.
I'm not talking about merging it to official SimpleORM, its just a cool features that i would like to have. 

Steeve