This three.js application uses an object of type THREE.PointCloud to
create a spherical cloud of points. The cloud can be animated.
A "Spin" animation makes the points rotate about the y-axis. Each
point rotates with its own random angular velocity. A "Drift" animation
gives the points arbitrary random velocities, but points are not allowed
to move too far out of the sphere.
The user controls the number of points and the size of each point.
The size is given in pixels. Note that a point is rendered as a square.
The animations look nice with a lot of points of very small size!