Added --nopk option for disabling the primary key

This can be helpful if the first column is not primary key. 

I tested both command and imported the scripts
+ php csv_to_sql.php inputfile.csv outputfile.sql database_name
+ php csv_to_sql.php inputfile.csv outputfile.sql database_name --nopk
and both are working flawless.  

This is the output of the file with --nopk specified:

CREATE  TABLE `test`.`test2` (
`990` VARCHAR(3),
`LIMA` VARCHAR(4)
) DEFAULT CHARACTER SET 'utf8';