Added --nopk option for disabling the primary key

[Jujhar]

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';

INSERT INTO test.test2 VALUES('991', 'LIMA');
INSERT INTO test.test2 VALUES('992', 'LIMA');