Fixes the Ord instance.

The previous version was not correctly counting
the number of digits of the numbers being compared.
Avoid creating larger numbers when comparing.

Instead of doing, say, compare (x * 10 ^ (delta-digits)) y, one
can compare (first delta-digits x) y and, when this matches,
we know that the final digits of y were 0 anyway.
Merge pull request #2 from jcpetruzza/fix-ord-instance

Fixes the Ord instance.