Support postgresql text array and execute function example

Two things here. Added text array as a special custom field value. 

Then I try to address postgresql functions. According to [this issue](https://github.com/npgsql/npgsql/issues/423), if you want to call a function with parameters and specify `dbCommand.CommandType = CommandType.StoredProcedure` then the only way to pass in the parameters is through `dbCommand.Parameters`. You can still set `CommandText` to a sql string to execute the function, but the command cannot be marked as `CommandType.StoredProcedure`

The ormlite extension points for ExecuteProcedure do not give me access to dbCommand in order to remove the `CommandType.StoredProcedure`. I created `ExecuteFunction` as a working example of executing a postgresql function with parameters according to Npgsql's docs. I don't know the right answer here. The separate, second method definitely does not feel right so maybe the override point for `ExecuteProcedure` needs to change.