Added a static css file with very ugly formatting.
I think I will move to dynamically generated css with
the Garden library in the near future.
Added dependencies for Garden css library.
Hasn't been configured yet.
Added a ring protocol. Be warned, ring does not inherit from the group
protocol because, to my knowledge, Clojure does not support that,
so it is possible to defrecord something that is a ring but not a group,
which is a mathematical impossibility.

Also added a zero-divisors function to return the set of zero divisors of
a ring.