Fix tests

The `Fractional` context of some functions was directly or indirectly resulting in defaulting of some of the doctests to `Double` instead of `Integer`, causing them to fail.

The ones that used the `empty` alias for `Empty` didn't really need a `Fractional` context, so I changed it to `Ord`.

Others used `nan`, which really requires `Fractional`. I changed the test cases by adding `.0` to the example numbers.

I added lines to the `.gitignore` file to facilitate development in a cabal sandbox. I hope this doesn't screw up anything on your end, but if it does then feel free to not take that change.