Exercise 7.1.3 should be simplified

Exercise 7.1.3 includes the lines:
```
first, *rest = list(words)
text = first
for word in rest:
```

Students are not familiar with this syntax and it should be replaced with:
```
text = words[0]
for word in words[1:]:
```

Also, parameter names `word` or `characters` make more sense since the function is invoked with a single word.