Chapter 7 exercises

The answer is... it is more efficient using 2 references. See 30cfe5ba1358f34ce7082c150b69bea68f2fb1c4 and c7a7d6d26120754e56e9da8d19de3d2f23a13835.

Run examples as:
`time perl exercise6.1.pl names.txt`
`time perl exercise6.pl names.txt`