=item calculate_area

The calculate_area function calculates the area of the
points passed in.  You can pass the points in a number of
different ways, but, regardless, you'll get the area back.

=over 4

=item *

You can pass in a series of points.  The function will
assume that the shape described is a closed-shape, that is,
the first point is automatically repeated as the end point.
You can pass in the points as perl6 pairs, e.g.:

    $area = calculate_area( $x0 => $y0, $x1 => $y1 );

or as two lists of x's and y's:

    $area = calculate_area( @x, @y );

or as a list of Point objects

    $area = calculate_area( @points );

=item *

You can pass in a Shape object.

    $area = calculate_area( $shape );

=item *

You can pass in an equation, and a beginning x-value and
an ending x-value, and the area will be that under the 
curve.  The area may be negative in this case.

    $area = calculate_area( $equation, $x0, $x1 );

=back

Returns: the area of the shape, in square units.

=cut