added Ord trait to GenericFraction

[DrAlta]

I made it so the NaN is less than everything else.

I needed this, so I can use fractions as the key to a BTreeMap.

[dnsl48]

Yep, looks good, thank you for the contribution!
The patch itself is looking alright, but there are some formatting issues, a couple of semantic things that clippy has picked up and perhaps a couple of tests are worth writing. We should be able to do this after this is merged, no worries 👍