Create the tables needed to store the information.

def _create(self, cache_file):
        """Create the tables needed to store the information."""
        conn = sqlite3.connect(cache_file)
        cur = conn.cursor()
        cur.execute("PRAGMA foreign_keys = ON")
        cur.execute('''
            CREATE TABLE jobs(
                hash TEXT NOT NULL UNIQUE PRIMARY KEY, description TEXT NOT NULL,
                last_run REAL, next_run REAL, last_run_result INTEGER)''')

        cur.execute('''
            CREATE TABLE history(
                hash TEXT, description TEXT, time REAL, result INTEGER,
                FOREIGN KEY(hash) REFERENCES jobs(hash))''')

        conn.commit()
        conn.close()