New introductory challenges!

We've added 3 new challenges to our beginning lessons:

• H is for Hopper: This one is designed to be the very first challenge that anyone does, and as a bonus, it introduces them to Hopper, our friendly beaver.
• Bucktooth Bunny: This challenge is the first test of variables, and whether they can use them to store a bunny's eye and teeth size.
• Funky Frog: This challenge is the second test of variables, and if they understand adding to them to make new values.

Besides the new challenges, we've also refined our feedback form to give us better information about the problems that users encounter, and we're using that to keep improving the challenges.