Add java.util.UUID serialier

This commit adds a UUID serializer/deserializer for java.util.UUID,
mirroring the structure of the existing `make-x-serializer`s.  The
UUID serializer uses the same procedure as the UUID serializer in
Cascading, i.e. write two longs, the most significant bits then the
least significant bits.

See also:

https://github.com/Cascading/meat-locker/blob/master/src/jvm/com/twitter/meatlocker/kryo/UUIDSerializer.java
https://github.com/magro/kryo-serializers/blob/master/src/main/java/de/javakaffee/kryoserializers/UUIDSerializer.java
Roundtrip namespaced keywords correctly

Keywords can be namespaced, e.g. :abc/def, and these are prominently
used in Datomic data structures.  Prior to this commit, namespaced
keywords would not roundtrip correctly: they would go in as :abc/def
and come out as :def, because of the way `(name :abc/def)` works.

This commit fixes namespaced keyword roundtripping by getting the
string name of the keyword from the `.-sym` method, which includes
the namespace in the returned string.

See also:

http://stackoverflow.com/questions/16594610/what-is-the-right-way-to-convert-a-namespaced-clojure-keyword-to-string
Merge pull request #4 from elliot42/serializers

Enable roundtrip serialization of namespaced keywords, java.util.UUID