Last Release with TurtleTypes

Until now we specified which turtle to use based on TurtleType - for now I've removed TurtleType and tried to simplify the turtle. I'm sure we'll go back and forth on some of this.

Also, josephlord suggested a nice introductory activity using targets so the next version includes targets.

On the other hand, I did want to capture this version as a release so here it is.

Thank you all for your feedback and help.