Fix some issues with Successible/Predessible

There are a few issues fixed here:

1. Remove the use of Numeric, since Double and Float really don't make sense.
2. Instead of requiring an Ordering, we just have a PartialOrdering as we only really need to compare items returned by next or prev. This is useful for cases like Vector clocks, which have a well defined next, but don't have a total Ordering.
3. Remove the specialized on these classes because Option and PartialOrdering are not specialized, so there is no win to having them specialized.
4. Put the laws in the algebird-test main code so they can be easily used by those wanting to test.