Remove an extra division

Currently, GHC does not merge `div` with `mod` by itself; `divMod` saves time.

Turn nested `if`s into `case`.
Merge pull request #10 from treeowl/master

Remove an extra division
Add support for `deepseq-1.4.0.0`

`deepseq-1.4.0.0`'s major change is the default `rnf` method implementation
(see haskell/deepseq#1 for details).

This commit changes `time` not to rely on the default implementation and
instead explicitly make use of `seq` like the old default implementation did.