Added AskSage() subroutine...

.. to ask SAGE to do computations during problem.authoring.  For example, you could use it to do this:
```     
Context("Matrix");
$python=<<END;
random_matrix(QQ,4,5,algorithm='echelonizable',rank=3).rows
END
$sage = AskSage($python);
$M = Matrix($sage);

$python2 =<<END;
matrix(QQ,$sage).rref().rows()
END
$sage2 = AskSage($python2);
$ans = Matrix($sage2);
Context()->texStrings;
BEGIN_TEXT

Row reduce \( $M \) $BR
\{ $ans->ans_array\}
END_TEXT
Context()->normalStrings;
ANS($ans->cmp());

```