Fix height, width, and area calculation

Clearly the height of a string is the number of lines
it contains, and therefore the width is the maximum line
length. That makes the area the number of lines times
the length of the longest line.

Signed-off-by: Doug Hellmann <doug.hellmann@gmail.com>
Merge pull request #1 from dhellmann/bug/width-and-height

Fix height, width, and area calculation