Created ch2 directory.

Moved all existing code into the ch2 directory.
3-1 Completed.
3-2 Completed.
3-3 Completed.

Most common error message was 'geom.erl:20: function area/3 already
defined', which indicated that I was using a period rather than a
semi-colon on the next to last pattern matcher.
3-4 Completed.