Implement circle projection and fix circle mtv.

shape.go

@@ -687,6 +687,12 @@ func (cp *ConvexPolygon) calculateMTV(contactSet *ContactSet, otherShape IShape)
 		smallest = Vector{center.X - verts[0].X, center.Y - verts[0].Y}
 		smallest = smallest.Unit().Scale(smallest.Magnitude() - other.radius)
 
+		// If the direction from target to source points opposite to the separation, invert the separation vector
+		// and set its magnitude to the diameter minus the original magnitude 
+		if cp.Center().Sub(other.position).Dot(smallest.Unit()) < 0 {
+			smallest = smallest.Unit().Scale(-other.radius * 2 + smallest.Magnitude())
+		} 
+
 	}
 
 	delta.X = smallest.X
@@ -835,6 +841,21 @@ func (circle *Circle) Bounds() (Vector, Vector) {
 	return Vector{circle.position.X - circle.radius, circle.position.Y - circle.radius}, Vector{circle.position.X + circle.radius, circle.position.Y + circle.radius}
 }
 
+func (circle *Circle) Project(axis Vector) Projection {
+	axis = axis.Unit()
+	projectedCenter := axis.Dot(circle.position)
+	projectedRadius := axis.Magnitude() * circle.radius * circle.scale
+
+	min := projectedCenter - projectedRadius 
+	max := projectedCenter + projectedRadius
+
+	if min > max {
+		min, max = max, min
+	}
+
+	return Projection{min, max}
+}
+
 // Intersection tests to see if a Circle intersects with the other given Shape. dx and dy are delta movement variables indicating
 // movement to be applied before the intersection check (thereby allowing you to see if a Shape would collide with another if it
 // were in a different relative location). If an Intersection is found, a ContactSet will be returned, giving information regarding