Diminish velocity when sliding

proportional to the sine of the difference between desired
and actual heading.
Add function to find line equation from two points
Add function to find intersection of two lines
Add function to find equation of perpendicular line given two points

Given 2 points A, B, find equation of the line which is perpendicular
to the line passing through A and B, and which intersects the midpoint
between A and B.
Add function to find circle from three points

Given three points assumed to be on the edge of circle, find the circle x, y, r