Fixed most jshint warnings

Remaining output:

```
~/Projects/cdo/mooc (jshint) $ grunt jshint
Running "jshint:all" (jshint) task
Linting src/maze/main.js ...ERROR
[L17:C5] W060: document.write can be a form of eval.
    document.write(mazepage.start({}, null, Maze.config));
Linting src/maze/maze.js ...ERROR
[L588:C5] W061: eval can be harmful.
    eval(code);
Linting src/turtle/main.js ...ERROR
[L21:C3] W060: document.write can be a form of eval.
  document.write(turtlepage.start({}, null, config));
Linting src/turtle/turtle.js ...ERROR
[L391:C5] W061: eval can be harmful.
    eval(Turtle.code);

Warning: Task "jshint:all" failed. Use --force to continue.

Aborted due to warnings.
```

The document.write lines can easily go away and I will probably replace the eval calls with `new Function()` since that's got some other advantages.

This caught a few small bugs, so I'll point those out in the github line comments.