Add support for prepared cursor

Add support for prepared cursors:

cursor= connection.cursor(Prepared=True)

When executing a SQL statement via cursor.execute() the first time, the sql statement will be parsed, prepared and executed. Subsequent calls to cursor.execute()`will irgnore the statement string, since it was already prepared but executing it again using the values specified in 2nd parameter of execute().

Example:

cursor= connection.cursor(Prepared=True)

cursor.execute("INSERT INTO t1 VALUES (?,?)", (1,2))

cursor.execute("INSERT INTO t1 VALUES (?,?)", (3,4))

# this will also work, since the sql statement will be ignored

cursor.execute("", (2,3))