Finding the orthocenter of a triangle in the plane: orthocenter

The orthocenter command finds the orthocenter of a triangle.

orthocenter takes one argument:
T, a triangle. The triange can also be specified with three points.
orthocenter(T) returns the orthocenter of T.

Example.
Input:

orthocenter(triangle(0,1+i,-1+i))

or:

orthocenter(0,1+i,-1+i)

Output:

which is the point (0,0), the orthocenter of the triangle.