Fixed syntax highlighting and wrong-property-used issue

[rishabh-ink]

a58c8eb

Under Exercise 3, the example for readCount was not using syntax highlighting.

Changed .property('@each') to .property('@each.read').

[rishabh-ink]

d807099

Split Exercise 3.4 into 3.4a and 3.4b. So it gives a visual cue to the learners that there are two steps to be completed. I, as a learner, who is going through the tutorial now, think that way.