add more generic limit and offset support to esqueleto for persistent-odbc

Hi,

Here is some code to add more generic limit and offset support utilizing an updated version of persistent (pull request #164). 
This is to support persistent using odbc for these dbms: mssql, oracle, mysql and postgres, each of which have different limit and offset syntax.
I wanted to get the sql that is generated by esqueleto and then decorate that sql with limit and offset depending on the backend dbms.
I am not entirely happy with the code I wrote for esqueleto and would welcome any feedback or hints.
The persistent-odbc code is at https://github.com/gbwey/persistent-odbc

Thanks,
Grant