Additional possible Turtle enhancements

[gwhitney]

This issue is a placeholder to keep other potential Turtle features that were not implemented for alpha so that they can be considered at some future date:

• Allow the color of a segment to depend on the sequence entry
• Allow the color of a segment to depend on the sequence index
• Allow mathjs formulas to compute the angle, step length, and or color of a segment, based on the entry and/or index
• For visualizers like Wait For It that retrace their own paths much of the time, add an option to show the "turtle" in each frame as well.
• A mode in which the view automatically pans, zooms, and/or rotates to keep the full path in view.
• Consider auto stopping the visualization if the turtle wanders too far off screen.
• When animating, provide some way to see the current values of the turn angles and step lengths as they change. That would make it easier to create a "still" of some frame of the animation that came out particularly attractive, or see what "special" angle it is that makes all of the traces of VFib Snowflake line up, etc.
• A 3D mode which has pitch and roll instructions as well as the current turn (yaw) instructions. In this mode, it should be possible to rotate the image in 3D.